Harry Potter's letter to Sirius Black (1995) I

This letter was written by Harry Potter to his godfather, Sirius Black, on Janurary 22 1995. The letter detailed the events of the previous night. Therefore it told Sirius of how Barty Crouch appered on the Marauder's Map in Severus Snape's storeroom, and Harry's encounter with Moody, Snape and Filch on the staircase.

Response
Sirius, in reponse to this letter, sent a letter of his own, simply saying "Send date of next Hogsmeade weekend by return owl."

Apperences
Harry Potter and the Goblet of Fire (Chapter 26 - The Second Task)