behind this door). the guards cannot jump the gap, so they will instead find their way through the fly swarm room. then they will get trapped by the hole in the center of the room, and cannot come back out. they may try to climb out, but they will be attacked by the fly swarm. so they will either be trapped or killed. before you try this, note however that you can lose some picks if you let guards with stuff on the belt to be killed this way.
so leave the fly swarm room and turn left to a bedroom. read the purple book on the table. it is a 