19

Mr. Kasparsnow brought everyone into the great hall and stood with his back to the tree.

“We begin again,” he said. “From the moment we left this room last night. I want the hour you went up, the route you took, and what you saw.”

Emily Brent said she practised until ten and went straight upstairs by the main stair. Professor Pawnsworth said he retired early and never came down again. Magnus Carolsen said he finished his game and went up by the main stair. Coalridge gave the hours of his rounds and the doors he tested.

Then Sir Basil spoke.

“I went up at eleven,” he said. “Main stair. I remember because I passed the grandfather clock and heard it strike eleven.”

Wesley cleared the chessboard and began to place pieces.

“This is the hall,” he said. “These are the stairs. And here is where each of you claims to have been,” he said while placing a bunch of pieces on the board. After completing the position, Wesley lifted a piece and, to everyone’s surprise, delivered a completely standard checkmate.

This is a directmate in 2 (yes, just a plain mate in 2). White to play and force a checkmate on the second move. After White's first move, you only need to show one of the continuations leading to mate. Here's Offerspill's Discord server.