 Murray Gold concurrently composed the score for the episode . In conjunction with new cues composed for the fourth series , Gold used some of his earlier work , such as Rose 's and Harriet Jones ' leitmotifs , the Ood 's " Song of Freedom " from " Planet of the Ood " , and the appearance fanfare for Mr Smith , the latter being played in diegesis . Gold discussed the new cues in the release of the fourth series soundtrack : 
