Crucible of Horror

An upper-class English home is ruled over by a sadistic, domineering father; the terrorized mother and her teenage daughter decide to plan a way to kill him. He is a stockbroker who takes great pleasure in making his wife's and daughter's lives a living hell. They drug and poison him, then dispose of his body. The mother is plagued by dreams of horror on the night of the murder, and continually sees visions of him. Their plan then seems to backfire when he comes back to life; he is seen the next day sitting at the breakfast table, acting his normal self, leaving his wife looking on in abject terror. The question is: did they go ahead with the murder, or was it just a dream?