Having left Leela (Louise Jameson) on Gallifrey, the Doctor (Tom Baker) and K9 Mark II (voice of John Leeson) don't remain footloose for long. The TARDIS is soon intercepted by the White Guardian (Cyril Luckham). The White Guardian sets the Doctor on an urgent mission to locate the six segments of the Key to Time, which are well disguised and hidden in odd corners of time and space. Once assembled, the Key will allow the White Guardian to restore balance to a universe descending into evil and chaos. To assist the Doctor the White Guardian has appointed Romana (Mary Tamm), fresh out of the Time Lord Academy and none too well traveled. Despite an initial bout of "negative empathy," the Doctor and Romana trace the first segment's signal to Ribos, a remote, backward planet that suffers from 32-year winters. There they are surprised to meet other interplanetary travelers, who include two conmen, Garron (Iain Cuthbertson) and Unstoffe (Nigel Plaskitt), and the Graff Vynda-K (Paul Seed), a warlord in the market for an inexpensive planet.