The Shout (1978)

When a wandering man named Crossley (Alan Bates) insinuates himself into the lives of British composer Anthony Fielding (John Hurt) and his wife, Rachel (Susannah York), the couple is cautiously hospitable. Isolated out in rural Devon, where Anthony works on his music, the Fieldings find that their enigmatic guest has some strange preoccupations, most notably an obsession with dark Aboriginal magic. Crossley claims that he can kill a person with a mystical shout, but is he telling the truth?