Acid Party (1969)
(Bell House Classics)
Big LSD shindig in Rome. As so happens in these tales, someone freaks out during the party and murders one of the other acid heads. Everyone is so high that no one discovers the body until the next morning. Also, no one has any clue who actually committed the murder including, apparently, the murderer himself. But then other members of the ill-fated acid party begin to die one by one as the killer tries to cover his tracks Agatha Christie style. Scenes of drug-crazed sex appear intermittently throughout. In a final confrontation, the last surviving witness knees the killer in the groin, causing him to lose his grip and fall to his death in front of a speeding train.