Bionic Woman and Merlin star Michelle Ryan plays the mysterious Lady Christina de Souza who joins the Doctor on a bus-trip which takes a very unexpected detour into danger. British comedy star Lee Evans also joins the cast playing a character called Malcolm whose life becomes connected to the Doctor's under extraordinary circumstances and Noma Dumezweni returns as Captain Erisa Magambo - last seen helping Rose and Donna save the world in Turn Left.

Written by Russell T Davies and Gareth Roberts.

Planet of the Dead is the first of four Doctor Who Specials which will air in 2009.

Bionic Woman and Merlin star Michelle Ryan

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