Back on Earth, the Doctor finds a clue in the search for the origins of the degeneration weapon. In his Sixth body, he meets Jackie Tyler and Lady Christina de Souza – thrown together by fate, or something more? – in pursuit of a powerful item of jewellery.

Meanwhile, a Time Lord renegade has duped Harry Sullivan into helping him stop the Doctor’s travels before they begin – and all are set on a collision course.

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