The Ribos Operation is the first serial of the 16th season of the British science fiction television series Doctor Who, which was first broadcast in four weekly parts on BBC1 from 2 to 23 September 1978. This serial introduces Mary Tamm as the companion Romana. The serial is set on the primitive and superstitious planet Ribos. In the serial, the exiled Emperor of Levithia, Graff Vynda-K (Paul Seed), seeks a piece of the rare element jethrik on the planet. At the same time, the Fourth Doctor (Tom Baker) and his travelling companion Romana (Mary Tamm) look for the first segment of the powerful Key to Time, disguised as the same jethrik piece. Plot The White Guardian recruits the Fourth Doctor to collect the six hidden and disguised segments of the powerful Key to Time. He assigns him an assistant Time Lady named Romanadvoratrelundar, whom the Doctor calls Romana. He warns him that the Black Guardian also seeks these segments, but for an evil purpose. The White Guardian provides them with a wand-like device, which can locate the pieces and remove their disguise. When inserted into the TARDIS console, the locator first reveals a segment to be on Cyrrenhis Minima, but then moves to Ribos. Ribos is an icy planet with late-medieval-type inhabitants who are unaware of alien cultures. A human from Earth named Garron tries to sell Ribos to an exiled tyrant called the Graff Vynda-K. The Graff is impressed by the planet's supposed quantity of jethrik, the rarest and most valued mineral in the galaxy. He believes the opportunity confirmed when he sees a piece of jethrik among the Ribos crown jewels. This is all part of a ruse orchestrated by Garron; the jethrik was planted by Garron's assistant Unstoffe, who also was playing a native with an "honest face" who spins a yarn to the Graff about a nearby lost mine. The locator points the Doctor and Romana to the same jethrik, which must be the disguised segment of the Key to Time. The Graff Vynda-K provides a large sum of money as a deposit for the planet that is to be kept safely in the room with the crown jewels, watched by Ribos guards by day and a shrivenzale beast by night. Later, Unstoffe distracts the shrivenzale, recovers their piece of jethrik, and takes the money from the safe. The Graff learns of Garron's deception when he