London, 2015. The Doctor's looking for a lost space probe. Lucie Miller's feeling just plain lost, on a world she no longer quite belongs to.
Perhaps there's someone who can help. A chance encounter with an old sparring partner leads Lucie to the Eightfold Truth — a bunch of crystal-bearing cranks who reckon a rebel sun is on its way to purge the Earth. As if!
But what if they're right?
The apocalypse is upon us. As humankind counts down the last days of its existence, the Doctor races to unmask the Eightfold Truth — and uncovers an old and deadly enemy.