Death and the Black Dog

"So make a deal with Death, Sirius Black." - What deal has our favorite animagus made with the guardian of the gateway from one world and another? And what about a first year Slytherin and his pale cat is bothering everyone around them? A mystery has found itself a home at Hogwarts, and provides a snarled skein for the Golden Trio and the Order to unravel.

Harry is intrigued by a new Slytherin student, who appears out of place in his new House, Snape is under the distinct impression there's something he doesn't want to know about this new student, and Hermione finds out something she isn't supposed to know. And what is with Nero's cat?

Harry talks to Nero, and finds out something important - if only he can remember what it is. Draco catches Nero coming in late, Hermione has a suspicion, and Dumbledore knows of a book with a clue to the puzzle that is Nero Letum. Oh, and we see more of Sirius's point of view.