Early one summer morning Isabel and her eleven-year-old daughter River walk across Regent's Park. They come across a rain-soaked man sitting alone on a bench and ask him if he's okay. But he doesn't know. In fact he doesn't know the answer to any of their questions; not even his own name. Urged on by her daughter Isabel takes the man to the hospital she works at, hoping that will be the end of it. But when the tests show there's nothing physically wrong with him, and yet he still can't remember who he is, she realises she can't walk away. Isabel made a promise to River that they would help this man, but with no way to identify him Isabel begins to worry about what he past secrets his memory loss might be hiding. Can they trust him?