Here's the synopsis! Sorry I was gone for so long!
Ch1: Hogwarts finds out about a fight between Snape and a former student (GG) when Malfoy peeks into his penseive. In the past it shows her arrival to Hogwarts and her first meeting with young Snape.
Ch2: Snape and GG's first lesson, where he finds out that she's a multiple animagus. In the present Hermione finds a siamese cat. The students are told about GG by McGonagall.
Ch3: A quick synopsis of GG's life with her unloving/somewhat abusive grandmother. Later, she and Snape figure out a new way to study Potions so that she can do better. In the present Snape gets mad at a mention of GG.
Ch4: In the past, GG is sorted into Gryffindor and begins her lessons. A cauldron blows up in potions and Snape watches over her in the hospital. In the present, Hagrid tells the trio about GG.
Ch5: Hermione's cat, injured by Filch, turns out to be GG. Snape takes her into his quarters so she won't be bothered by students. She wakes up and she and Snape talk a bit. Turns out they were lovers.
Ch6: In the past, GG wakes up in the hospital wing, were she talks with Snape. Dumbledore reveals that Snape had loved GG since the exploding cauldron incident.
Ch7: In the present GG insists that they continue their relationship despite changes in Snape's appearence and life. So he asks GG to marry him.
Ch8: GG helps a drunken Snape into bed. She's apparently troubling him.
Ch9: Snape reveals to GG that he is in love with her.
Ch10: She agrees to enter into a forbidden relationship with Snape.
Ch11: GG purposefully flunks in potions so that she and Snape could have 'private lessons.'
Ch12: Snape decides to go with GG for Christmas. They start to make out when they are interupted by another teacher. GG takes an invisibility potion. Directly afterwards one of GG's friends comes in and, when the potion wears off, discovers the disheveled Gabriella.
Ch13: Annabelle shouts at and insults GG and Snape. Snape erases her memories, but is unable to erase her changed feelings about GG.
Ch14: GG and Snape arrive at g'ma's house. G'ma chases Snape, the stranger with a frying pan before GG stops her. G'ma finds out that Snape and GG are in a relationship even though he is a teacher. Snape makes G'ma promise not to tell.
Ch15: Snape and GG exchange presents (GG recieves special spellbook and Snape gets a ring.) At the party Snape gets jealous and tells the entire group of people that he and GG are in a romantic relationship, just in time for Dumbledore to step in.
Ch16: Dumbledore performs a spell that shows that GG and Snape truly love one another. They cannot continue their lessons, but they can see one another. In the present, GG says yes to marrying Snape, but they are told by Dumbledore that she must resume classes. They decide to openly admit their relationship anyway, and GG prepares to be reinstated to the school.
Ta-da! I tried to skim it down as much as possible, but that's hard to do with so long a story. Here's the bare bones, none the less!