 A key component of the episode is the return of Rose Tyler, portrayed by Billie Piper. Piper's return was planned during filming of the second series; in January 2006, Piper made a pact promising to return to film several more episodes. Davies and Piper cited her other projects — specifically, her roles as Belle de Jour in Secret Diary of a Call Girl, the eponymous character in the BBC adaptations of Philip Pullman's Sally Lockhart quartet, and Fanny Price in the ITV adaptation of Mansfield Park — to explain that her departure was permanent. Davies created the expectation of Rose's return by mentioning her in dialogue and featuring Piper in cameo appearances in "Partners in Crime", "The Poison Sky", and "Midnight".
