The new synopsis - 3 part version

Sophie (+ Paul)
For Sophie and Paul, it is over. They have had an ideal relationship and Paul struggles to understand how it went wrong. But for Sophie, that she is with Paul is down to chance. This means that good or bad could easily be reversed. All that stands in the way of these other possibilities is fear.
Claire, her friend, cannot understand how Sophie could throw Paul and a great relationship away. She is resentful, and reminds Sophie that it could've been her, Claire, that was with Paul. She could've been happy.
Paul recognises the danger to themselves - 'We are not an accident' - but it is too late. Sophie finds a way to overcome her fear and discovers another possible life.

Claire (-Paul)
In this story Claire has what she wanted. Paul. But they argue, Paul frustrated that Claire really is not committed or passionate about them together. Can Claire really change?
She sees her chance when her sister drops by unexpectedly. She is going away to get away from Nick, her boyfriend. He is too much. Can Claire look after her flat?
In Natalie's flat Claire finds photos of Nick. He has an intensity that is missing from her relationship with Paul. She decides to take a chance. She leaves Paul - just disappears and moves into Natalie's flat. And then she goes picking up the threads of Natalie's life, her friends, and work colleagues, and Nick. Her pretext is apologising for Natalie's bad behaviour, but her motive is to become someone else.
But can Claire finally change?

Paul (-Claire)
With Sophie, Paul knew who he was and what he wanted, but with Claire he is another man. For Paul, Claire's reticence and secrecy are part of her inability to commit to their relationship, driving Paul to despair. For Paul, his relationships are fundamental to who he is as a person. Perhaps out of peevishness, or just confusion he spends the night with a stranger, and returns in the morning, wondering about the consequences. But Claire has disappeared. He begins to search for her and his first visit is Sophie. Looking beyond her hostility he is struck by the unfairness of chance: he could've been with Sophie, he could've been someone else. Feeling the weight of this injustice, his life goes into a spiral. Paul indeed becomes someone else. He is unrecognisable.