knight's move

Exploration Stage: Mansion of Illusions
From: Kira Woodville
Description: The first item on Thomas' list appears to be a key of some kind. The first was a chess piece, located near the groove in the table. Can I place it here?
Completed: The knight's piece fit perfectly! You heard a click. It seems that some mechanism has moved inside the table. It must be part of a more complicated key that we haven't found yet.