Ocelot

Eleven-year-old Sirius Black is thrilled to begin Hogwarts, in large part because he wants to get away from his abusive, bigoted family. He hopes that his family will not impede him from making friends, or cause him to be Sorted into Slytherin. To his delight, he ends up in Gryffindor with his three new friends, James Potter, Remus Lupin and Peter Pettigrew. At the opening feast, Sirius's favorite cousin Andromeda and some of the other older Gryffindor students tell the four first-years a bit about Hogwarts and the staff.

Sirius survived the Battle of the Department of Mysteries and is now living as a free man with Ted and Andromeda Tonks. Harry finds himself performing accidental Legilimency. Lupin is back as DADA teacher, Professor Binns has moved on, and the new History of Magic teacher is a brilliant, politically progressive young American woman of mixed ethnicity. She teaches the class about the roots of magic, the history of Wizard-Muggle relations, the rise of Voldemort and the first war, and more. The captured Death Eaters are at Azkaban, but with only Aurors to hold them there Draco Malfoy hopes that his father will soon escape.

July 1972: The summer after his first year at Hogwarts, Sirius is forced by his parents to attend Bellatrix's wedding to Rodolphus Lestrange. Bellatrix and Rodolphus have just graduated Hogwarts, so they invite their school gang, including Snape. Sirius's whole family is there, including his kindly cousin Andromeda and wonderful uncle Alphard. But there's something afoot with the bride and groom and their entourage...

Gives background (as I imagined it) of Sirius' parents. One day, when Sirius is five-and-a-half, he learns his first lesson about the cruelty and injustice of his parents.