Alex Edgbert – A 13 (nearly 14) year-old wizard and Gryffindor, who is the brains of the group and believes in Sirius' innocence.

Harry Potter – A 13-year-old wizard who became famous in the wizarding community by surviving a powerful curse from the most powerful dark wizard of all time.

Ron Weasley – Alex's godbrother and second cousin and the youngest son of the Weasley family, who owns Scabbers.

Hermione Granger – Alex and Harry's other best friend who is bookish and clever, who is the second brains of the group.

Kate Nguyen – Alex's crush and best friend who believes (but not solidly) his claims that Sirius is innocent.

Matt Crocitto – Alex's best friend and Gryffindor third-year.

Lord Voldemort – The most powerful dark wizard of all time, who started a war that lasted for 11 years and killed Harry's parents.

Remus Lupin / Moony – Alex's godfather and honorary uncle, a member of the Marauders, Sirius' best friend, and the new Defense Against the Dark Arts teacher at Hogwarts, who is secretly a werewolf, but initially, only Alex and Hermione know this fact.

Sirius Black / Padfoot – Alex's godfather and maternal uncle, a member of the Marauders and Remus' best friend who recently escaped Azkaban and many people believe is after Harry. Alex and his mother, Desiree, are the only members of the wizarding community besides Sirius and Remus to believe in his innocence.

Rubeus Hagrid – The Gamekeeper who also acquired the job of Care of Magical Creatures professor and a good friend of the group.

Peter Pettigrew / Scabbers / Wormtail – Ron's pet rat who is revealed to be the true servant of Voldemort who ratted out his parents to Voldemort. He escapes from the Dementors to serve Voldemort again.

Desiree Deuyour – An Auror and member of the Marauders, as well as Alex's mother and Sirius' younger sister.

Albus Dumbledore – The Headmaster of Hogwarts who believes in Sirius' innocence.

Sybil Trelawney – The Divination professor at Hogwarts who is inaccurate and a fraud at making predictions, though she does make a prophecy.

Minerva McGonagall – The Head of Gryffindor House and Transfiguration professor who is strict but concerned woman and a lifelong fan of Quidditch.

Severus Snape – Alex's godfather and honorary uncle, the Head of Slytherin House and Potions professor, who takes pleasure in getting Harry in trouble and favors Alex in class.

Filius Flitwick – The Head of Ravenclaw House and Charms professor.

Draco Malfoy – Harry's rival and Alex's first cousin who frames Buckbeak for harming him and has his death ordered.

Lucius Malfoy – Draco's father who has influence in the Ministry.

Ginny Weasley – Ron's younger sister who has a crush on Harry.

Percy Weasley – The Head Boy of Gryffindor and Ron's older brother, who is in his last year at Hogwarts.

Fred and George Weasley – Ron's older twin brothers who are well-known pranksters and Beaters for the Gryffindor Quidditch team.

Molly Weasley – Ron's mother who is kind and overprotective of Alex and Harry.

Arthur Weasley – Ron's Muggle-obsessed father who is the Head of the Misuse of Muggle Artifacts Office.

The Dursleys – Harry's abusive family.

Lily and James Potter – Harry's parents who were killed by Voldemort protecting Harry.

Argus Filch – The grumpy caretaker of Hogwarts who has a sadistic pleasure in tormenting students.

Mrs. Norris – Filch's beloved cat.

Cornelius Fudge – The Minister of Magic, who is big-headed and believes that Hogwarts needs to be protected against Sirius.

Oliver Wood – The captain and Keeper of the Gryffindor Quidditch team, who is in his final year.

Cedric Diggory – A fifth-year Hufflepuff Perfect and the captain and Seeker of the Hufflepuff Quidditch team.

Cho Chang – The Ravenclaw Seeker who Harry is immediately smitten with.

Neville Longbottom – Alex's godbrother, friend, and second cousin.

Crabbe and Goyle – Malfoy's dimwitted minions.

Penelope Clearwater – A seventh-year Ravenclaw and Percy's girlfriend.

Madam Rosmerta – The barmaid of the Three Broomsticks