A promise made in haste. A search for lost memories. Three lives changed forever.

Early one morning, Isabel and her eleven-year-old daughter River are walking across Regents Park when they come across a distraught-looking man sitting on a bench. They ask him if he's OK, but he doesn't know the answer. In fact he doesn't know the answer to any of their questions - he doesn't even know his name.

Urged on by her daughter, Isabel takes the man to hospital and hopes 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. With no ID on him, she will have to call the authorities but there's a look of fear in the man's eyes and she knows that's the last thing he wants. Isabel begins to worry about what he might be hiding about his past but she also made a promise to River that they would help this man. Can they trust him? And how far is she prepared to go to keep her word to her only child?