 On 23 March 2013 , BBC released a short prequel video to the episode , written by Steven Moffat . In the prequel , the 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 . 
