the red house mystery

by A. A. Milne

Something's happened," said Cayley. He was breathing quickly. "I heard a shot-it sounded like a shot - I was in the library. A loud bang - I didn't know what it was. And the door's locked." He rattled the handle again, and shook it. "Open the door!" he cried. "I say, Mark, what is it? Open the door!