While in mid-flight, the Doctors Tardis suddenly stops and he hears a calling from outside of the Tardis. The Doctor realizes only a Guardian could have so much power, so he accepts the invitation to step out of the Tardis. The Guardian is sending the Doctor on a mission to search for the Key of Time. With the Key, the White Guardian will be able to restore balance to the universe.
Despite his objections, the Doctor is given a new companion to help him on his quest for the six segments of the Key of Time. Before leaving, the Guardian reminds the Doctor there is also a black guardian who wants the Key for evil purposes. The Doctor is to trust no one. Heading back to the Tardis, he finds Romana already inside the Tardis. However, she claims the President of Gallifrey sent her on this mission.
The couple are given a 'tracer' which connects to the Tardis and draws it to the nearest segment of the Key of Time. The pieces have been disguised as ordinary objects. Once landing on the planet, the tracer can be disconnected from the Tardis and helps locate the hidden piece. While investigating the planet Ribos, they run into a couple of con artists named Garron and Unstoffe.
Things turn sour when the con artists intended target, the Graff Vynda-K discovers he's being conned. The 'intelligent' man that he is, Graff deduces the Doctor and Romana are working alongside Garron. He orders their capture, but Unstoffe manages to escape. He befriends Binro, an outcast on the 'backward' planet for believing the stars in the sky are not jewels, and they may not be alone in the universe.
When Unstoffe confirms Binro's theory, he agrees to help Unstoffe escape. To do so they enter the catacombs. Meanwhile the Doctor has summoned K-9 and with his help, escape along with Romana & Garron. Unwilling to accept defeat, Graff follows everyone into the catacombs. He manages to kill Binro, but soon after there is a cave in and the Graffs guards all die and he accidentally blows himself up.
With the situation now over, the Doctor departs with an expensive piece of jethrik owned by Garron, which he had used to con the Graff that Ribos was an expensive planet. Garron tries to steal back the jethrik, but the Doctor manages to switch it with a piece of stone. Once safely in the Tardis, Romana used the tracer to transform the jethrik into the first piece of the Key of Time.
PLANET OF ORIGIN: Gallifrey, era uncertain.
REASON FOR JOINING: Was asked by the 'President of Gallifrey' to help the Doctor on his quest for the Key of Time.
NEXT: Armageddon Day