Alan and Tricia Hamilton (David Tennant and Sarah Parish) are very happy. He's the head of a building firm and on top of his game. She's a part-time beautician and mother to their two sons. One day their perfect, if unremarkable, life is torn apart when a last-minute decision to pop out for a quick drink with a colleague sees Alan step out in front of a passing car. The resulting accident leaves him in a deep coma but with remarkably few physical injuries. Desperately worried about him, Tricia is delighted when he comes round – only to discover that the man she loved has disappeared. His behaviour's changed, he's lost all of his inhibitions and he veers from angry and frustrated to vulnerable and childlike. Simple tasks like making toast and getting dressed are beyond him, he's unable to hold down the job he loves and he plays and laughs with his sons as if he's a child. Alan's behaviour puts his relationship with Tricia under intolerable pressure. She longs to find the husband she loves in there somewhere – but fears she may have lost him forever.