Night Must Fall by Emlyn Williams

 A secluded British cottage.

A dead body in the woods.

A strange visitor at the door.

...and night will fall soon!

When the imperious, embittered Mrs. Bramson learns that her young maid Dora is pregnant, she summons the child's presumed father to her bungalow. The young man, Dan, is charming but mysterious. Could he be responsible for the recent murder and beheading of a local woman, and could Mrs. Bramson be his next victim? Skillfully, Dan insinuates himself into Mrs. Bramson's affections and attemps to seduce her skeptical niece, Olivia. Despite strong suspicions of Dan's diabolical intentions, Olivia finds herself attracted to, and fascinated by, the young man.