I won't summarise the plot, this has been done ad nauseam, usually by the people who insist that the movie is stupid and not worth watching. If you haven't seen the film yet, you're better off going in blind. You may hate it, but you'll get much more out of it if you have a chance to go along with the journey and decide for yourself it's merits and meaning.

Instead I just want to posit a theory to bare in mind if watching for a second time...

I think that the return of Tim Roth is occurring entirely in Rebecca Hall's mind as she struggles and fails to come to terms with her daughter's pregnancy, growing up and moving away.

The inability to come to terms with the loss of her first baby is such a traumatic stressor that her mind retreats to it when it cannot cope with the impending 'loss' of another child. Her mental pain is rationalised by her as a return to the physical abusive pain that she experienced as a young woman.

In the final scene that is often taken as a dying hallucination she finallyaccepts the pregnancy and loss, handing the baby to it's mother who is moving out and moving on with her life.

Tim Roth is the avatar of her emotional breakdown but by killing him she is killing and coming to terms with her current emotional trauma.

There's little that's explicit in the film to necessarily support this reading but it's the conclusion that the ending made me come to.

Even if I'm barking up the wrong tree and twisting my mind into a strange kindness, I think it's an interesting thing to consider.

Your opinion of course may vary!

For years you've found a home where you feel safe, you have a daughter and you live in a nice place, you're confident and kind, a better life you could not find, until the past returns, reoccupies your space. You do your best to be polite and move him on, but it's clear this beast won't leave, and won't be gone, anguish, turmoil then ensue, just what can you really do, to this manipulative, controlling past demon.

Rebecca Hall is brilliant as a woman being haunted by a sinister past partner, who carries with him the torment she endured during their time together, and is intent on delivering more pain and agony.