The Doctor and Donna are trapped on board a mysterious spacecraft. Fate of the crew: unknown. Fate of the universe if what’s on board gets out: terminal.

Chance. Misfortune. Coincidence. These are the weapons of choice for the Doctor’s latest enemies. And those enemies are very, very hungry. For Ruby Sunday, this Christmas Eve is a birthday she’ll never forget. It’s the day she joins the Doctor on board a Goblin ship. The day she learns of dangers from beyond the universe. The day her life really begins...or, perhaps, the day it ends.

What links a diamond raid in 20th Century London, a secret base in the heart of the city's sewer system, a cold and desolate planet light years from Earth, and a daring plan to alter the entire course of interplanetary history? The Doctor's old enemy, Lytton, has allied himself with the Cybermen. Their scheme, if successful, could bring the human race to its knees. For the Cybermen have journeyed back in time to prevent the destruction of their home world. And for Mondas to survive, the Earth must die.

The hugely powerful Key to Time has been split into six segments, all of which have been disguised and hidden throughout time and space. Now the even more powerful White Guardian wants the Doctor to find the pieces. With the first segment successfully retrieved, the Doctor, Romana and K9 trace the second segment of the Key to the planet Calufrax. But when they arrive at exactly the right point in space, they find themselves on exactly the wrong planet - Zanak.

The travellers arrive in the dangerous domain of the Toymaker, where their failure to win at a series of games could result in them becoming his playthings for eternity. Apparently innocuous nursery characters reveal deadly intent, and for companions Steven and Dodo the stakes are raised with every game of blind man's buff and musical chairs. The Doctor, meanwhile, is rendered invisible and given the challenge of completing the fiendishly difficult Trilogic game.