When Did You See Her Last - Lemony Snicket

S. Theodora Markson and Lemony Snicket are called to the Knight household: housemaids Zada and Zora are worried about the disappearance of Cleo Knight. Cleo's parents are permanently dazed and confused, which Lemony realizes is because their doctor is injecting them with laudanum. In Cleo's room, Lemony finds a failed attempt at making invisible ink.