When all communication is lost from Mars Probe 7 after it begins its trip back to Earth, a second craft is launched to investigate. As Recovery 7 docks in space, it too loses all communication. The Doctor and UNIT are given the task of investigating the mystery as Recovery 7 returns to Earth.
It appears that no one can be trusted, as the space capsule is hijacked from its UNIT convoy with military precision. What has happened to the missing astronauts? Could this be a secret invasion from Mars – or is the enemy much closer to home?
This story has been restored to full colour. Special features Include: commentary, a featurette about the trials and tribulations of making and restoring the story, a look back at the Third Doctor, trailer, photo gallery, subtitle production notes, Radio Times listings (PDF)