The Ten-Minute Window
Could the thief reach the room, take the treaty, and vanish inside Percy's coffee break? Time it.
The theft fit inside minutes: side door, staircase, an unlocked room. Set the distances and see how wide the window really was.
Drawn from The Naval Treaty (The Memoirs of Sherlock Holmes, 1893) — read the summary & analysis, or try Who Took the Treaty?, this story's game. More at the Game Room and the tool bench.