A killer has been stalking the streets of Glasgow. Busman Boab drives an old double-decker bus kitted out with a variety of deadly booby traps, serving an enigmatic greater purpose by carrying doomed passengers to their final destination. Mr. Dig, Sinkhill's fox-masked vigilante defender, and Charlotte, the scarred survivor of a vicious encounter with the terrifying blue van clowns, have teamed up to bring Boab's reign of terror to an end. But Boab has some tricks up his sleeve, and a few formidable friends...