Siobhan O' Malley is a woman assisting Abed Cahal at the Clanbronwyn Hotel, in Trilby's Notes, after studying antiques under him at Warwick University. She is described as having a forceful personality, and is the first to figure out that "Terrance Railby" is actually Trilby . Her ancestor, Jacob O'Malley, owned the shipping company which transported a crate made from wood of Jack Frehorn's harpsichord. She expresses great interest in Trilby's quest, and despite his warnings, manages to follow Trilby into the World of Magick. He gives her tranquilizers as a way back to the World of Technology. She eventually follows him to the stump of Cabadath's tree, where they are both captured and restrained so as to be used in Agent Lenkmann's ritual to summon Cabadath. Trilby thwarts Lenkmann's plans by willing himself to die, and is shown to later have been resuscitated by Siobhan.