"Missy's Theme" is a leitmotif composed by Murray Gold. It accompanies the female incarnation of the Master portrayed by Michelle Gomez during series 8, 9, and 10 of Doctor Who.
The piece is made mostly of synths and sounds dreamlike, evoking Missy's relation to the heaven-like Nethersphere in Series 8. It is led by the vocals of Halia Meguid, whose voice, although singing English lyrics, is heavily altered to sound like a hidden or reversed message fading in and out of the ethereal instrumental.
The piece first appears in The Caretaker when Seb welcomes CSO Matthew to the Nethersphere, and reappears in subsequent scenes involving Missy and the Nethersphere during Series 8, and also in Empress of Mars
An ominous arrangement of the theme is also heard during Missy's meeting with Clara in The Magician's Apprentice, and another orchestral arrangement is later heard in The Lie of the Land.
Both the main version of "Missy's Theme" and an extended concert arrangement were included on the Series 8 soundtrack, along with other variations of the theme appearing in other tracks. The concert arrangement, although released on the Series 8 soundtrack, only made an appearance in an episode by Series 10's The Lie of the Land.