Dr. Cranley
Dr. Cranley, an English scientist specializing in experimental food preservation techniques, was the father of Flora Cranley. He had in his employ Dr. Jack Griffin and Dr. Arthur Kemp to help him in his research, the former being Flora's fiance. When Griffin disappeared suddenly and was gone for months, Cranley initially did not think much of it because Griffin had told him he wished to do his own research in privacy.
However, at the insistence of Flora, he and Kemp looked into Griffin's disappearance and discovered disturbing evidence that his assistant was experimenting with the drug known as monocane. Cranley, who knew about the drug, became terrified and went immediately to see Inspector Lane to report Griffin's disappearance. Unfortunately, he was too late, as Griffin had used the monocane to make himself invisible and begun a violent killing spree.
Along with Flora, Cranley tried to speak to Griffin to talk some sense into his assistant, but before he could do so, a panicky Kemp foolishly alerted the police to Griffin's location, and Griffin was forced to flee. The next time Cranley would see his assistant would be when he was on his deathbed, killed by a bullet from Inspector Lane's gun.
