Harry and Lucy's marriage has become dull and monotonous - no matter how much they love each other, they can't seem to refind that spark.
Harry reluctantly agrees to a threesome with a man Lucy finds online to try and restore some magic to their sex life.
But what happens when they wake in the morning to find he's still there?
What happens when Ben decides he doesn't want to leave?
And what happens when they realise Ben isn't the man he said he was...