Tough narcotics detective 'Popeye' Doyle is in hot pursuit of a suave French drug dealer who may be the key to a huge heroin-smuggling operation.

When a charming 12-year-old girl takes on the characteristics and voices of others, doctors say there is nothing they can do. As people begin to die, the girl's mother realizes her daughter has been possessed by the devil--and that her daughter's only possible hope lies with two priests and the ancient rite of demonic exorcism.