Ron: Let me get this strait. Sirius Black has escaped from Azkaban to come after you? Harry: Yeah. Hermione: But they'll catch Black, won't they? I mean, everyone's looking for him. Ron: Sure. Except no one's ever broken out of Azkaban before, and he's a murderous raving lunatic. Harry: Thanks, Ron.
On the train back to Hogwarts Harry tells Hermione and Ron of his predicament.