Late last night, the curator of the London Rare Book Archive discovered that a priceless Holmes manuscript was stolen. The only evidence left behind was a single folded note:

The thief arrived at 8 PM, left at 8:45, and passed through three consecutive rooms without being seen. Each room has exactly two doors (one entry, one exit). The corridor cameras record only when someone enters or leaves a room. The timestamps we have are:

• 8:00 PM – A person enters Room A (from hallway).

• 8:15 PM – A person leaves Room B (to hallway).

• 8:30 PM – A person enters Room C (from hallway).

• 8:35 PM – A person leaves Room A (to hallway).

• 8:40 PM – A person leaves Room C (to hallway).

We know:

1. The thief moved through Rooms A, B, and C in some order—never revisiting a room.

2. They did not trigger a camera in the hallway except at the very start (8:00 PM) and the very end (8:45 PM when they left the last room).

3. Exactly one camera reading corresponds to the thief—every other camera event was unrelated.

Question: Which room was broken into, and how do you know?

Send answers to sherlock@tcd.game