The idea here is that the characters find a poltergeist in the first room which asks "Which one of these is as dumb as a door?"

The characters need to leave the room, search the library how each of the kings died, and verify which one was killed by an intellect devourer. (or pass a hard history check).

Guessing right allows them to calm down the poltergeist, guessing wrong means the poltergeist throws one of them around and tries to lock them into the room.