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In the third episode of the four-part story "The Ribos Operation," the Doctor (Tom Baker) has located the first missing segment of the Key to Time on the planet Ribos. Unfortunately, the planet may fall into the hands of the sinister Graff Vinda-K (Paul Seed), thanks to a pair of confidence tricksters named Garran (Iain Cuthbertson) and Unstoffe (Nigel Plaskitt). Could all this skullduggery be the handiwork of the yet-unseen Black Guardian, who is determined to prevent the reassembly of the Key -- and, by extension, the restoration of the balance between Good and Evil? Originally telecast on Septmeber 16 1978, "The Ribos Operation, Episode 3" was written by Robert Holmes.