Theo can neither talk nor read or write, because twenty-four years ago a shooting accident left him aphasic. But was it an accident or was the young man trying to take his own life? And if so, was his motive related to the recent disappearance of his sister, Lucy? At the memorial service for her politician husband, Elen Holden offers journalist Simon a proposition: find out what happened to her children and she will provide him with information regarding her husband's dealings in Westminster. However, with Theo unable to communicate and Lucy missing, the only way Simon can uncover the truth is by giving Theo his voice. He starts by interviewing the siblings' friends and his colleagues in the press, who lead him through a maze of half-truths and lies to an unexpected conclusion that forces Simon to question the ethics of his profession. And he meets Theo and his devoted carer, who shows Simon Theo's paintings, one of which intrigues him. With the painting in mind, Simon explores the effects and treatment of aphasia, coming to understand there is an outside chance Lucy holds the key to unlocking Theo's Voice. All he has to do is find her.