Then:

Back at university Dominic makes a drunken pact with Lucy: if neither of us are married by 35, let's marry each other.

Now:

They are 35. And they are considering if it could actually work. Dominic's quit life as a brilliant New York ad exec and moved back to London to find out. Lucy is a single mother and doesn't know whether to take him seriously.

The proposal would be ideal - if only he wasn't already married, she hadn't tried marriage once before, and their sex wasn't quite so bad...

Can friendship be redesigned to make a marriage?

Or is there too much excess baggage?