Night Slaves [1970] [DVD]

A disillusioned man tired of the grind of life takes his wife (who loves another man) to a small town to start over. At night in the small town, he discovers that the residents (and his wife) become mindless zombies bent on a mysterious task, of which he can discover nothing. He does discover a strange woman who also doesn't become a zombie, He tries to solve the mystery, but finds himself under suspicion of murder.