THE MISSING LANTERN LENS
At 8:10 p.m., someone opened the locked display cabinet in the fictional Harbor Museum and took its brass lighthouse lens. Which of the three suspects opened the cabinet?

Suspects:
Sol: a volunteer at the ticket desk.
Rue: a workshop assistant.
Vale: a lighting technician.

Clue 1: The only route from the workrooms to the cabinet passed beneath an open skylight. Rain fell continuously from 8:00 to 8:30 p.m. Anyone who visited the cabinet at 8:10 would have wet sleeves.
Clue 2: At 8:15, Sol had dry sleeves. Rue and Vale both had wet sleeves.
Clue 3: The cabinet latch leaves violet chalk on the right thumb of anyone who opens it. At 8:15, Rue's thumbs were clean. Vale had violet chalk on the right thumb. Nobody washed their hands between 8:10 and 8:15.

Answer key for the game builder, NOT for display before a guess: Vale. Sol cannot have crossed the wet route. Rue crossed the route but could not have opened the chalk-marking cabinet with clean thumbs. Vale has both required traces. This case has exactly one correct suspect. An incorrect guess can be tried again.