Synopsis: Crash-landing on an asteroid, the Doctor, John and Gillian meet Grig a Therovian. Grig is on a quest to save his people from a weakening illness and enlists the travellers to collect a vital moss from the dangerous ice planet, Ixon.
Synopsis: The Doctor is invited to Dowmphilly tracking station to observe the launch of a new space platform. However, the platform is in fact a launch pad for a nuclear arsenal. When a mysterious object is detected approaching earth it is assumed to be a meteor and, despite the Doctor's warnings, the space platform use it as target practice for a nuclear missile. As the missile has no effect it soon becomes clear that the object is a spacecraft, In retaliation, the space platform is apparently destroyed. Fearful that the Earth has instigated a space war what it cannot hope to win, the Doctor travels in the TARDIS to the alien vessel to confront its unseen occupants.