Doc gets crowned president, Gallifrey gets invaded twice, and Leela and K-9 get no goodbye
The Doctor signs an agreement with some aliens in their cosy, egg-themed base but Leela hasn’t been invited to the party. She was left in the TARDIS with K9, who has a handle on what’s going on but isn’t being at all cooperative. The Doc’s agreement appears to involve becoming the president of Gallifrey because before we know it that’s where we are and the Time Lords are soon ushering in the Age of the Doctor.
But it’s all an elaborate ploy to disable Gallifrey’s global defence shields and facilitate an invasion force of three to beam down to the surface and demand the immediate disabling of Gallifrey’s global defence shields. A different alien invasion force is masterminding this one, though, and this six-part season closer soon turns into an intra-relativistic Hanna Barbera game of cat and mouse.
And as promised, behold The Evolution of The Sontarans (mental note: good title for a future audiobook!):