Earth - a small, insignificant planet. Entirely devoid of intelligent life.
At least that's according to the legal documents. The Doctor, Romana and K9 find themselves at the centre of a most unusual trial.
An intergalactic corporation wants to bulldoze the planet for a development project. Only a previous court's preservation document is standing in their way. The Doctor has been summoned as an expert witness. If he can prove Earth contains intelligent life, the whole world will be saved.
But with a fortune at stake, it was never going to be that simple.