life debt?

[pern_dragon]

Okay, I need to know where, and from whom, Harry finds out about James saving Snape from being attacked by Remus when he went to the Shrieking Shack after Sirius set him up. Forgive me, but I don't actually own all of the books. *hides* I will, however, be more than thrilled to go check out whichever books I need to from the library to read the appropriate passages again for loving detail. While the Lexicon is an amazing place, and I've spent hours on it searching for other info, for this one, I just figured I'd ask folk who might know off the tops of their heads. Thanks so much in advance!
Nicole aka Good_Witch on Ashwinder and ThePetulantPoetess