The TARDIS returns Tegan to Heathrow Airport: Tall trees, peaceful, clear skies, thriving vegetation and a touch of sulfur in the air. Obviously the TARDIS is a little out of date (about three hundred years or so), but upon looking around the Doctor finds there's more amiss than his navigational controls, all arising after a recent comet crash that was not on Earth's schedule.

The Doctor makes the fugitive Terileptils a rare offer they shouldn't refuse; but, though few in numbers, they have a plan in the works for the quick and complete domination of Earth and mean to see it through.