Alison is a marriage mender. Her job is to help couples who fear they have reached the end of the line. But the trouble with spending your time sorting out other people's problems is that you tend to take your eye off your own. Even when her husband's ex Lydia arrives on the doorstep demanding to see her son, Alison thinks she can handle it. But what Alison doesn't realise is that Lydia is the one person who has the ability to destroy their happy family. And sometimes the cracks can run so deep that even a marriage mender can't repair them.