Alexander "Alex" Michael Wayne Deuyour is an American-born English wizard who was born while on vacation at Disneyland in Anaheim, California on September 24, 1979 to Desiree Deuyour (née Black) and her husband, whose last name was Deuyour. Deuyour was killed during the height of the First Wizarding War, being killed by Lord Voldemort himself. When Alex was born, only his mother, father, and godfathers Sirius Black, Remus Lupin, Severus Snape, and James Potter were there. Desiree went to Hogwarts from 1971 to 1978 and was the adopted sister of James Potter and member of the Marauders as a Gryffindor. Her older brother was Sirius Black, making him Alex's godfather and maternal uncle. Although she ran around at the age of 16 along with Sirius, she was not disowned by the family. When she was married to Alex's father, she lied to her parents Walburga and Orion about her husband, claiming that he was a pure-blood, when he was in fact a half-blood. Neither of her parents discovered this fact. Desiree was upset when she discovered her younger brother Regulus was killed by Voldemort. When Alex was three months old, a prophecy was named about him and Harry Potter as the prophecy said that he would help a boy, either Harry or Neville Longbottom, both of whom were his second cousins and godbrothers. Desiree was upset when James and Lily Potter, her close friends, were killed, but unlike most of the wizarding world, she did not believe Sirius betrayed them as she was told that Peter was the Secret-Keeper.
Alex spent most of his life being taught that blood purity didn't matter. Desiree desperately tried to keep connections with her family, but with the exception of Andromeda Tonks, her husband Ted, and their daughter Nymphadora, none of them wanted contact with her. Alex met and became friends with Ron Weasley when he was three and went to the Muggle primary school St. Gregory's, where he met his godbrother Harry Potter and his cousin, Dudley Dursley. Alex did not tell Harry of their relationship until he went to Hogwarts as well but stood up to Dudley. He was often beat up for this but he did use his magic to stop the beatings.
When Walburga died in 1989, Desiree was made Heiress to the House of Black. She disowned Orion for his cruel mistreatment of Sirius as a child, and he died in 1990. She reinstated Sirius to the family tree and disowned Bellatrix Lestrange for being a Death Eater. She made a law stating that if anybody in the family were affiliated to Death Eaters, they would be removed from the family. Lucius and Narcissa were subsequently removed as well. Among those reinstated were Andromeda, Sirius and Desiree's uncle, Alphard, the Longbottoms, and the Weasleys, something Walburga and her loyal house-elf Kreacher were displeased about.
On the first weekend of July, Alex got his acceptance letter to Hogwarts, which his mother was proud about. They went to Diagon Alley a couple of weeks later, and while getting his school supplies, Alex ran into his godbrother twice: first, while eavesdropping on Harry and Hagrid, unbeknownst to them and the second at Madam Malkin's, where Alex also met his first cousin, Draco. Either time, he did not reintroduce himself to Harry, as he was afraid that Harry would resent him. On September 1, 1991, Alex befriended Harry, who was not irritated. In fact, he was a little confused of why Alex did not tell Harry who he was at their primary school, but Alex says that there is a law against violating the Statute of Secrecy. Alex also meets his other godbrother, Ron, and the three become friends. The group is later added upon with the addition of Kate Nguyen. Alex also befriends Muggle-born student Hermione Granger, much to Ron's dismay. At school, all five of them are sorted into Gryffindor. Alex also befriends the half-blood Matt Crocitto, who is bullied due to his blood status by Malfoy and his cronies, Vincent Crabbe and Gregory Goyle.
Alex improves his magical abilities at school, and is the instant favorite of most teachers: including Filius Flitwick, Minerva McGonagall, and Severus Snape, his godfather and honorary uncle. Alex also makes the position of Chaser on the Gryffindor Quidditch team, along with Harry making the position of Seeker. Alex tells Harry that his father was a Chaser himself, something Harry is shocked to hear. Enraged that Alex and Harry are still attending the school, Malfoy challenges them to a duel, which Ron accepts on their behalf. This is later revealed to be a trap, and Alex, Harry, Ron, Hermione, Kate, Neville, and Matt barely avoid trouble from Filch by escaping into the third-floor corridor, where they discover a three-headed dog, which Alex identifies as a Cerberus, a dog from Greek mythology that guards the gates of Hades/The Underworld. Alex indicates that the two share a similarity as the dog is guarding a trapdoor.
On Halloween, Ron makes fun of Hermione bossing him around, which causes her to hide in the girls' bathroom. Later that night, Quirrell claimed there was a troll in the dungeons and Alex, Harry, Ron, and Kate save Hermione. Hermione protects the four from punishment by lying to the teachers. Harry and Alex then participate in their Quidditch match against Slytherin, during which Hermione, Ron, and Kate see Snape supposedly jinxing Harry's broom. Alex also noted that Quirrell was muttering something, and suspects him instead. Hagrid accidentally lets slip that the thing that Fluffy, the three-headed dog, is guarding is between Professor Dumbledore and Nicholas Flamel, which causes the group to become suspicious. Alex remembers that Flamel is a name on Dumbledore's Chocolate Frog card, and that he discovered alchemy with Dumbledore and Alex correctly deduces that the Philosopher's Stone is what is being guarded in the chambers. Before the next Quidditch match, Alex finds out that Snape is refereeing the next Quidditch match against Hufflepuff, but Alex points out that this is a way to keep Quirrell from jinxing Harry's broom again. Gryffindor wins. After the match, Alex, Harry, Ron, and Hermione discover Hagrid is reading a book about breeding dragons, which Alex and Ron are concerned about, since dragons are illegal to breed. They discover that Hagrid is breeding a Norwegian Ridgeback, which he affectionately names Norbert. Alex convince him to send it to Ron's older brother, Charlie, since he works at a dragon reserve in Romania. Hagrid reluctantly agrees, but the group are caught out of bed by Filch when Harry accidentally leaves his Invisibility Cloak on the Astronomy Tower. The group (excluding Ron, who is in the Hospital Wing suffering from a dragon bite), along with Neville, Matt, and Draco are sentenced to detention. There, they discover that Voldemort is drinking unicorn blood to keep himself alive. After suspecting that Quirrell (or in Harry, Ron, Hermione, and Kate's case, Snape) is using the Philosopher's Stone to bring Voldemort back, they decide to stop him. They get past the Devil's Snare, flying keys, wizards chess board, a troll that is already knocked down, and a potions riddle. Alex and Harry face Quirrell, who is trying to take the Philosopher's Stone for Voldemort. They pass out and awake in the Hospital Wing, learning that Quirrell was accidentally burned to death by Harry and that Voldemort retreated back to Albania. They also learn that Dumbledore has destroyed the Philosopher's Stone, meaning that Flamel can die. Dumbledore says that Voldemort could still come back and says that Ron, Hermione, and Kate are safe. At the end-of-term feast, Dumbledore gives Alex, Harry, Ron, Hermione, Kate, and Neville last-minute points, allowing them to beat Slytherin and win the House Cup. Heading back, Alex assures his friends that he will keep in contact with them as Harry states that Hogwarts is his home.
On July 31, 1992, Alex Deuyour learns from his mother, Desiree, that the Ministry of Magic detected Harry using magic at the Dursleys. Concerned, he sends a letter to his friends Ron Weasley, Hermione Granger, Kate Nguyen, and Matt Crocitto, who has decided to join the group. Alex joins Ron and his brothers, twins Fred and George, to rescue Harry from the abusive Dursleys using Ron's father, Arthur's bewitched Ford Anglia. They take him to the Weasleys' home, the Burrow. Alex, Harry, and the Weasley family travel to Diagon Alley for school supplies. They run into Hermione and Kate and meet Lucius Malfoy, father of Draco, and also Gilderoy Lockhart, a conceited autobiographer and adventurer who is the new Defence Against the Dark Arts professor. At King's Cross station, Alex, Harry, and Ron enter Platform 9 and miss the Hogwarts Express. They fly in Mr Weasley's car to Hogwarts, crashing into the Whomping Willow on school grounds and damaging Ron's wand. The car then escapes into the forest.
Later, Harry is the only one who hears a strange voice emanating from the castle walls. Soon after, Mr Filch's cat, Mrs Norris, is found petrified, along with a bloody warning scrawled on a wall: "The Chamber of Secrets has been opened. Enemies of the heir, beware". Salazar Slytherin, one of the school's founders, created the Chamber after a dispute with fellow founders on admitting Muggle-born students. Some in the wizarding community disdain Muggle-born wizards like Hermione, believing pure-bloods are superior. The Chamber supposedly houses a monster that only the Heir of Slytherin can control.
During a Quidditch game, a rogue Bludger strikes Alex and Harry, breaking their arms. Lockhart blunders an attempt to repair them, sending Alex and Harry to the hospital overnight. Dobby, a house-elf that was responsible for Harry being accused of using magic at the Dursleys, visits Harry and Alex and reveals he jinxed the Bludger and sealed the portal at King's Cross. He says the Chamber of Secrets was once opened years before. Dobby also tells them that house-elves like himself serve one master their entire life, and cannot be freed unless given proper clothing. After another attack, students attend a defensive duelling class, during which Harry exhibits a rare ability to speak "Parseltongue", the language of snakes.
Harry, Ron, Hermione, Kate, and Matt suspect Draco is the Heir, given his hostility toward Muggle-borns. Alex however points out that Draco has to be the heir of Salazar Slytherin and says that the Malfoys are not related to Salazar Slytherin. Despite this, Hermione brews Polyjuice Potion, allowing Alex, Harry, Ron, Kate, and Matt to impersonates Draco's friends, Blaise Zabini, Goyle, Crabbe, Pansy Parkinson, and Theodore Nott. They learn that Draco knows nothing about the heir. Meanwhile, Moaning Myrtle, a ghost that haunts a girls' bathroom, shows the group a diary left in her stall. It belonged to Tom Riddle, a student who witnessed another student's death during the Chamber's previous opening. Riddle's consciousness within the diary claims that Hagrid was responsible. Hermione is petrified in the next attack. The school is put on lockdown and may close. Headmaster Albus Dumbledore is forced out and Hagrid is sent to Azkaban prison.
Following instructions left by Hagrid, Alex, Harry, Ron, Kate, and Matt follow spiders into the Forbidden Forest. They encounter Aragog, a gigantic Acromantula which denies its involvement, and claims spiders fear the real monster. Aragog attempts to feed Alex, Harry, Ron, Kate, and Matt to its progeny, but Mr Weasley's car rescues them. Alex correctly deduces that due to Harry speaking Parseltongue and hearing it before the attacks, the monster is a Basilisk, a giant snake whose direct gaze kills and petrifies victim when seen indirectly through a secondary reflection. Alex is proven correct when Alex, Harry, Ron, Kate, and Matt discover that Hermione deduced this as well. The basilisk is the voice in the walls, and it travels through the plumbing. Moaning Myrtle was the student that was killed.
Ron's sister Ginny is abducted and taken into the Chamber. Harry, Ron, Kate, and Matt discover the entrance in Myrtle's bathroom, and much to Alex's dismay (as he correctly deduces that Lockhart was a fraud), force Lockhart to enter it with them. Lockhart confesses he is a fraud who made up all of his stories and attempts to erase the group's memory after stealing Ron's damaged wand. The spell backfires, obliterating his own memory, and causes a cave-in; Ron, Kate, and Matt are separated from Alex and Harry and the former three stay behind to help Lockhart.
Alex and Harry proceed to the Chamber and find an unconscious Ginny. A manifestation of Tom Riddle reveals he is Lord Voldemort and the Heir of Slytherin, which Alex correctly deduced after noting his fear in the flashback, something Harry did not notice. He opened the Chamber and framed Hagrid. He has been using the diary to possess and control Ginny, who had been behaving strangely. The basilisk appears to kill Alex and Harry. Dumbledore's phoenix Fawkes arrives, bringing Alex and Harry the Sorting Hat. Fawkes blinds the basilisk and Alex and Harry pull the Sword of Godric Gryffindor from the Sorting Hat. They slay the Basilisk but are poisoned by its venom. As Riddle taunts the dying Alex and Harry, Fawkes' tears heal them. Harry and Alex stab Riddle's diary with a severed Basilisk fang, destroying it and Riddle's body, and reviving Ginny.
Alex, Harry, Ron, Kate, Matt, Ginny, and Lockhart return to the castle. Alex and Harry give the diary to Dumbledore. Lucius bursts in, furious that Dumbledore returned. He is accompanied by Dobby, who is the Malfoys' house-elf and was working to protect Alex and Harry. Alex points out that Lucius slipped the diary into Ginny's cauldron while they were in Diagon Alley to open the Chamber. Alex and Harry trick Lucius into freeing Dobby from servitude by giving him their socks; Lucius attempts to attack Alex and Harry in revenge, but Dobby repels him.
The petrified students are cured, Gryffindor wins the House Cup again, Hagrid is released, Lockhart is confined to St. Mungo's Hospital, and Alex is happy to share what happened that school year with his mother.
During summer holidays in 1993, Alex Deuyour sends a birthday card to his friend Harry Potter and learns that the Weasleys are in Egypt visiting Ron Weasley's brother, Bill, who works as a Curse-Breaker at Gringotts. Alex and his mother, Desiree, learn that Sirius Black has escaped Azkaban. Secretly, they are ecstatic despite Minister Fudge wanting Desiree to capture Sirius, her older brother, and she reluctantly agrees. Meanwhile, Desiree has to return to the United Kingdom, following on a report that Harry lost his temper and used his magic on his uncle's sister, Marge. Alex calls out the Dursleys for their treatment of Harry.
Desiree and Alex spend the rest of the summer at the Leaky Cauldron, where they reunite with Harry and on the last night, the Weasleys, Hermione Granger, Kate Nguyen, and Matt Crocitto. Harry is concerned after eavesdropping on a conversation between Arthur and Molly and learns that Sirius has supposedly escaped Azkaban to kill Harry, but Alex tells him the truth.
At Hogwarts, the guards of Azkaban, known as the Dementors, patrol the school looking for Black. Alex and Harry are unusually affected by their presence, and ask help from Remus Lupin, the new Defence Against the Dark Arts teacher, in learning to repel them. Lupin teaches Alex and Harry the incredibly difficult Patronus charm, but Alex and Harry are able to produce full-bodied Patronuses to fight the Dementors. Meanwhile, Black is reported to have been sighted in the village of Hogsmeade, close to Hogwarts.
Harry is given a secret map by Fred and George Weasley, which reveals everyone inside the castle and its grounds. Harry uses it to sneak into Hogsmeade without permission. Hiding inside a pub, he overhears a conversation in which he learns that Black is actually his godfather, and that he killed his own best friend, Peter Pettigrew, while also betraying Harry's father, James, to Voldemort.
Alex tells the group that he and his mother do not believe that Sirius betrayed James and that he is innocent, though Harry, Ron, and Hermione do not believe this.
Alex, Harry, Ron, Hermione, Kate, and Att visit Hagrid at his hut, and are surprised to find Ron's missing pet rat, Scabbers, hiding there. As they walk back to the castle with Scabbers, Ron is attacked by a large dog. The dog drags Ron into a secret tunnel and disappears, coming out on the other side, inside the Shrieking Shack in Hogsmeade. The dog is revealed to be Black in his Animagus form.
Alex, Harry, Hermione, Kate, and Matt reach the Shack, followed by Lupin and Alex's pet pit bull, Bandit, the former of whom spots them on Harry's map. Lupin disarms Harry, then explains why he believes Black to be innocent. Black claims that the crimes attributed to him were actually committed by Pettigrew, who escaped suspicion by faking his own death. Pettigrew is also an Animagus, and has been hiding as Ron's rat Scabbers this whole time. Harry suggests handing Pettigrew over to the Dementors. Alex embraces Sirius, who reveals to the shocked group is also his godfather and maternal uncle, as he is his mother's older brother.
While walking back to the castle, the full moon suddenly emerges and Lupin, secretly a werewolf, starts transforming. Black turns into the dog to protect the others, and Pettigrew escapes amid the chaos. Alex, Harry, Hermione, and Black are accosted by Dementors, and Black ends up being captured.
While Black is held captive inside a tower in Hogwarts, Dumbledore confirms with Alex, Harry, Hermione, Kate, and Matt that he is indeed innocent. He instructs them to save Black, by going back in time and setting him free, before he is handed over to the Dementors. Using a Time Turner, which Hermione has had since the beginning of the year to get to all her classes, they travel back a few hours. Present-day Alex and Harry save their past selves, and the past versions of Hermione and Black from Dementors using a Patronus. They then allow Black to be captured by Snape, before using Hagrid's hippogriff, Buckbeak, to release him from the tower and escape.
The next day, Lupin is forced to resign as his secret identity as a werewolf is now known to the school. Harry is upset at not spending more time with his godfather, Black, but Dumbledore asks him to take comfort in having saved his life. On the train journey back to London, Harry receives a letter from Black, who also sends a replacement pet owl for Ron.
Over the summer, the Weasleys invite Alex Deuyour and Harry Potter (along with Hermione Granger, Kate Nguyen, and Matt Crocitto) to attend the Quidditch World Cup final, played between Bulgaria and the Republic of Ireland. The match ends in a victory for the Irish, but the campsite is attacked by Voldemort's former followers called the Death Eaters. Nobody is killed, but the Dark Mark is set off and found to have been cast by Barty Crouch's house-elf, Winky.
Hogwarts reopens and a new tournament is announced between three schools to compete for the Triwizard Cup. The other competing schools are Beauxbatons and Durmstrang. Students excitedly await the start of the Tournament, which is declared open after the visiting teams arrive. The Goblet of Fire, a magical object tasked with selecting the champions, is unveiled. It names three champions, one from each of the schools, and then select Alex and Harry as its fourth and fifth champions, despite the two being underage.
The students perceive Alex and Harry have cheated and turn on them. Rubeus Hagrid believes in Alex and Harry's innocence and shows them the dragons involved in the First Task. Alex and Harry alert Cedric Diggory, son of Amos Diggory, to the challenge and they are helped "Mad-Eye" Moody, ex-Auror and the new Defence Against the Dark Arts teacher, to prepare for the task. Using their superior flying skills, Alex and Harry get past the dragon and retrieve a clue for the next task.
A Yule Ball is announced and Alex and Harry must find a partner, as champions traditionally commence the opening dance. Alex asks Kate as a friend to the Yule Ball, while Harry and his best friend Ron Weasley struggle to get dates but end up with Parvati and Padma Patil. Ron gets jealous seeing Hermione Granger, who he has a crush on, with Viktor Krum, the Durmstrang champion, and spends the night arguing with her. Harry is sullen that Cho Chang is with Cedric, the other Hogwarts champion.
The Second Task requires saving a close friend or relative from the lake. Alex and Harry use Gillyweed, given to them by Dobby, to breathe underwater. Alex rescues Kate and Matt from the lake, while Harry rescues Ron from the lake, while also saving the Beauxbatons champion Fleur Delacour's sister out of fear that she will drown if Fleur cannot rescue her in time. After the task, Alex tells Harry that he believes that Igor Karkaroff or Barty Crouch Sr. put their names in the Goblet of Fire. Alex, Harry, and Krum discover a seemingly mad Barty Crouch on the Hogwarts grounds, but he has vanished when they return.
The Quidditch field is prepared for the Third (and final) Task, and requires champions to overcome a maze filled with obstacles. Alex, Harry, and Cedric succeed in reaching the centre, where the Triwizard Cup is placed. They touch it together, but are transported outside Hogwarts to a Muggle graveyard. Cedric believes this is part of the Task, but Alex and Harry get alerted when the latter's scar starts burning wildly. Wormtail arrives with Lord Voldemort and kills Cedric with the latter's wand. Subduing the injured and gagged Alex and Harry to Thomas Riddle Sr's grave, he then uses Harry's blood to restore a frail Voldemort back to his full, physical body. Voldemort summons his Death Eaters and tries to kill Alex (which is revealed in the next book to be because the prophecy says that an friend of Harry's will help him defeat Voldemort) and Harry in front of them. He fails when his and Harry's wand streams of green and red connect, in a rare phenomenon called Priori Incantatem. This causes a distraction by seeming to summon the ghosts of those that Lord Voldemort's wand has killed, including Harry's parents and Alex's father Thomas, allowing Alex and Harry to escape back to Hogwarts using the Cup.
At Hogwarts, Moody pull Alex and Harry into his office to question them and the two realize he is a Death Eater and he put his name in the Goblet of Fire. Alex realizes that he is not the real Moody. They are saved by the arrival of Professors Dumbledore, McGonagall, and Snape, who force Moody to reveal himself to be Barty Crouch Jr., a Death Eater formerly presumed dead. He had been imprisoned in Azkaban for supporting Voldemort and had escaped by leaving his mother in his place using Polyjuice Potion. Crouch Jr. had then been placed under the Imperius Curse by his father until he had managed to break out of it during the Quidditch World Cup and cast the Dark Mark. He had then imprisoned the real Moody and impersonated him using more Polyjuice Potion. Arriving at Hogwarts, he made sure that Alex and Harry won the tournament and were transported to the graveyard for Voldemort's ritual; his only wish is that Voldemort rise to the power he once had. His father had been placed under the Imperius Curse after Crouch Jr.'s escape, but had started to resist it and so had been killed.
Crouch Jr. is handed over to the Dementors. Alex and Harry recover in the hospital wing, surrounded by Ron, Hermione, Kate, Matt, and the Weasleys. They meet with Cedric's grieving parents, while Dumbledore makes plans to prepare the wizarding world for Voldemort's return. The school year ends and Harry returns to live with the Dursleys again for the summer, while Alex returns home with Sirius and his mother, Desiree.
During the summer holidays, Alex Deuyour and his mother, Desiree, and Alex's godfather and maternal uncle, Sirius Black, host Grimmauld Place as the headquarters of the Order of the Phoenix. Alex has been happy and content with staying with his friends Ron Weasley, Hermione Granger, Kate Nguyen, and Matt Crocitto. However, like the rest of his friends, he finds it difficult to send vague letters to Harry, which frustrates him. One evening, they find out that the Ministry has expelled Harry for using the Patronus Charm in front of his cousin, Dudley, but Dumbledore resolves this by convincing Fudge to give Harry a fair trial. After that, the Advance Guard takes Harry from Privet Drive to Grimmauld Place by tricking the Dursleys. Alex, Ron, Hermione, Kate, and Matt tell Harry that the Order is a secret organization that Dumbledore created to fight Voldemort and the Death Eaters. Alex and Harry want to join but are still too young.
The Ministry of Magic, under Cornelius Fudge, attempt to malign Alex and Harry for stating that Voldemort has returned. Harry is also charged with performing underage magic while with a Muggle, but is exonerated and returns to Hogwarts. Dolores Umbridge, a senior Ministry employee, is the new Defence Against the Dark Arts teacher. She initiates strict rules and a textbook-only curriculum and forbids the students from practicing defensive spells. Alex, Harry, Ron, Hermione, Kate, and Matt form a secret student Defense group called Dumbledore's Army. The group secretly meets in the Room of Requirement to practice under Harry's instruction.
One night, Harry dreams that Arthur Weasley is attacked by Voldemort's snake, Nagini. His vision is true, and Arthur is found seriously injured at the Ministry. Dumbledore realizes that Harry and Voldemort's minds are connected, and he orders Professor Snape to teach Harry Occlumency, a skill to close one's mind against others. Umbridge is tipped-off about Dumbledore's Army; to prevent Alex and Harry's expulsion, Dumbledore claims responsibility for forming the group. To avoid arrest, he goes into hiding. Umbridge is appointed headmistress, though she is magically barred from entering Dumbledore's tower. She begins enacting strict rules and regulations and attempts to dismiss Professor Trelawney.
Harry's Occlumency lessons go poorly. During his Ordinary Wizarding Level (OWL) exams, he envisions Voldemort torturing Sirius in the Department of Mysteries at the Ministry. Alex and Harry attempt to contact Sirius at Grimmauld Place, using the Floo Network in Umbridge's office, but she catches and interrogates him, threatening to use the Cruciatus Curse on him. Hermione intervenes by concocting a story that leads them into the Forbidden Forest. Umbridge provokes the centaurs, who take her captive.
Alex (though he tells Snape where they're going), Harry, Ron, Hermione, Kate, Matt, Ginny, Neville, and Luna fly to the Ministry to save Sirius, but he is not in the Department of Mysteries. Instead, the room in his vision has shelves filled with glass spheres, one of which bears Harry, Alex, and Voldemort's names. Alex and Harry pick it up and are immediately surrounded by Death Eaters. Lucius Malfoy reveals that Harry was lured there by a fake vision from Voldemort, and that he wishes to hear the prophecy contained in the glass sphere. He asks Alex and Harry for the sphere, but they refuse. The Hogwarts group fight the Death Eaters and evade them. Order of the Phoenix members (tipped off by Professor Snape) arrive and battle the Death Eaters. Neville accidentally drops the prophecy sphere, breaking it. Alex stuns Bellatrix Lestrange to save Sirius from death, but Bellatrix escapes, with Harry following her, followed closely by Alex and Sirius. Sirius is cleared of all charges after seeing Sirius try to cast the Stunning Charm on Voldemort.
Voldemort appears and tries to kill Alex and Harry, but Dumbledore appears and thwarts him. Fudge and other Ministry of Magic employees arrive on the scene and witness Voldemort just before he escapes. In his office, Dumbledore tells Alex and Harry the prophecy was made by Professor Trelawney, who predicted the birth of a child with power against Voldemort and that one of the child's friends would help them overthrow Voldemort. This caused Voldemort to pursue Harry's parents, and is why he targets Alex and Harry. Overwhelmed by the prophecy, Alex and Harry reunite with Sirius, who tells them that they are now officially a family. Harry grows sullen, but the wizarding community believes and respects him. Supported by his friends, Harry is able to endure another summer with the Dursleys until Sirius and Remus Lupin come to pick him up for the rest of his life.
Desiree Deuyour and her son, Alex Deuyour, spend the rest of the summer holidays at the Weasleys' home, the Burrow, with Alex's friends Ron Weasley, Hermione Granger, Kate Nguyen, Matt Crocitto, and Ginny Weasley. One night, Albus Dumbledore arrives with Alex's second cousin and friend Harry Potter and Alex's godfather and maternal uncle, Sirius Black and Remus Lupin. Elsewhere, Bellatrix Lestrange and her sister Narcissa Malfoy secretly seek out Severus Snape at his home. Narcissa asks Snape to make an Unbreakable Vow to protect her son, Draco, and to carry out a task, should he fail.
While school shopping in Diagon Alley, Alex, Harry, Ron, Hermione, Kate, and Matt observe Draco suspiciously slipping into Knockturn Alley. On the Hogwarts Express, Alex and Harry, wearing the latter's Invisibility Cloak, overhear Draco claim he may not return to Hogwarts the following year to instead, "go on to better things." Alex and Harry suspect that Draco may have become a Death Eater, but their friends extensively deny this, much to their dismay. During the Welcome Feast, Slughorn is introduced as the new Potions teacher while Snape is now the Defence Against the Dark Arts instructor. Alex, Harry, and Ron take Slughorn's advanced potions class. Harry finds a tattered potions textbook bearing the inscription, "The Half-Blood Prince." The book contains tips, as well as new spells, scribbled in the book margins that yield better results than the printed instructions. With it, Harry rises to the top of the class and wins a vial of Felix Felicis, a luck-enhancing potion. Hermione says Harry is cheating while Slughorn compares his potions skill to his mother, Lily.
Dumbledore begins tutoring Alex and Harry on Tom Riddle, the younger version of Lord Voldemort, to prepare them for their foretold battle. He shows Alex and Harry memories of Riddle's past, including his meeting young Riddle in an orphanage. One memory from Slughorn's early Hogwarts' days suddenly goes dark when Riddle utters the word, "horcrux". This memory has been altered, and Dumbledore tasks Alex and Harry with retrieving the true one. To that end, Alex and Harry attend the Slug Club, an informal group of Slughorn's favorite students. Hermione, Kate, Matt, and Ginny are also included, but Ron is excluded.
Hermione invites Ron to Slughorn's Christmas party, but he remains upset about her previous relationship with Viktor Krum and begins seeing Lavender Brown, inducing strong jealousy in Hermione. Harry takes Luna Lovegood and Alex takes Kate to the party but Alex and Harry leave early to follow Draco Malfoy when he gatecrashes the event. Shortly after, Ron is poisoned drinking mead that Slughorn had intended as a gift for Dumbledore. Ron survives but while he is in the infirmary, Lavender breaks up with him when he favors Hermione. Also, Harry and Ginny and Alex and Kate become romantically involved.
Using the Felix Felicis potion, Alex and Harry successfully obtain Slughorn's unaltered memory. It reveals how Tom Riddle created six Horcruxes to become immortal. Horcruxes, magical objects encasing one's soul, are created with ancient dark magic. Two, Riddle's diary and a ring, have been destroyed, but Dumbledore believes four Horcruxes remain.
Dumbledore discovers another Horcrux location, and Alex, Harry, and Dumbledore journey to a remote cave. Inside, a Horcrux is hidden under protective enchantments in the middle of a lake. Dumbledore nearly dies retrieving a Locket Horcrux. Returning to Hogwarts, Alex, Dumbledore, and Harry see the Dark Mark hovering above the Astronomy Tower. Atop the tower, they hear footsteps approaching. Dumbledore casts a protective spell on Alex and Harry, forcing them to watch helplessly when Draco arrives and disarms Dumbledore. A distressed Draco reveals that Voldemort ordered him to murder Dumbledore. He is unable to follow through, however; Snape arrives and casts the Killing Curse at Dumbledore.
Released from Dumbledore's protection, Harry pursues Snape (with a reluctant and conflicted Alex following him), firing a curse at him. Snape easily deflects it. Snape taunts Harry for using his own spell against him and reveals that he is the Half-Blood Prince. Snape escapes with Draco through the ensuing battle between Death Eaters and the Order of the Phoenix. Dumbledore's lifeless body is found at the base of Astronomy Tower. Representatives from all wizarding races attend his funeral. Later, Alex and Harry discover that the Locket Horcrux is fake, switched by someone whose initials are, R.A.B. Ron, Hermione, Kate, and Matt vow to help Alex and Harry find and destroy the remaining Horcruxes. To protect Ginny, Harry ends their relationship. To protect Kate, Alex also ends their relationship but promises to resume it once the war has concluded.