Mike Mignola and Dark Horse present the complete saga in four volumes, from Hollow Earth to King Fear. In 2001, Hellboy quit the B.P.R.D., leaving Abe Sapien, Liz Sherman and a bizarre roster of special agents to defend the world from occult threats and the growing menace of the frog army. Plague Of Frogs, which ran concurrently with other volumes in the B.P.R.D. series, explores the fate of the unit after Hellboy's departure, cracks open the secrets of Abe Sapien's origin and sets the war on frogs in motion.