A biker gang visits a monastery where they encounter black-robed monks engaged in worshipping Satan. When the monks try to persuade one of the female bikers, Helen, to become a satanic sacrifice the bikers smash up the monastery and leave. The monks have the last laugh, though, as Helen, as a result of the satanic rituals, is now possessed and at night changes into a werewolf, with dire results for the biker gang.

A fifteen-year-old boy wants to buy a gun from an adult racketeer named Priest, in order to become president of the gang to which he belongs, and to return them to active "bopping" (gang fighting) which has declined in Harlem.