The Woman Who Wouldn't Die (1965)

Starring Gary Merrill, Jane Merrow, Georgina Cookson, Neil McCallum, Rachel Thomas
Directed by Gordon Hessler
(actor & director credits courtesy IMDB.com)

A female executive's domineering ways lead her husband and one of her employees to conspire to murder her, but once they've done the deed, the husband fears she may have returned from the dead.

Although pretty derivative of past works, this is an absorbing and intricately plotted thriller with strong performances.  I enjoyed it, and must admit I didn't see the screenplay's final twist coming, but was somewhat disappointed that the filmmakers didn't try to do more to amp up the horror, although there are some effectively creepy moments.  Hessler would go on to make a series of violent horror films with Vincent Price, so it's interesting to see him create chills on a more subtle level here, including a nice sequence where Merrill witnesses lights turn out one by one in a house he had thought empty.  Still, I felt the picture was a bit too dialed back, and would have been much more memorable with a greater emphasis on unnerving the audience.