The Truth Serum is a tool used by Ledroptha Curtain in the 2nd book, The Mysterious Benedict Society and the Perilous Journey. He uses the truth serum on Nicholas Benedict, in at attempts to get him to reveal the location of the duskwort. When this plan fails, he kidnaps the Mysterious Benedict Society and uses a fake version of the truth serum on himself to attempt to trick Mr. Benedict into thinking he was telling the truth when he was lying. Constance Contraire uses her ESP to reveal that it is a trick.