A little girl finds the Doctor sitting on a swing in a playground. They discuss that he is sad because he can't find his "friend".
On 23 March 2013, the BBC released a short prequel video to the episode, written by Steven Moffat. In the prequel, the Eleventh Doctor is sitting at the swings of a children's playground when he meets a little girl. They talk about losing things, and the Doctor states that he has lost someone twice and he hopes he might be able to find her again. The girl tells him that, when she loses something, she goes to a quiet place for a think, and then can remember where she put it. As the girl leaves, it is revealed that she is Clara Oswald.