The Doctor and UNIT investigate Ruby's past. But as the Time Window reveals horrifying secrets from Christmas Eve, the mysterious Triad Technology unleash the greatest evil of all.

The Doctor has lost, his ageless enemy reigns supreme, and a shadow is falling over creation. Nothing can stop the devastation... except, perhaps, one woman.

Traps are sprung and old enemies unite as the Doctor and Belinda finally arrive home to find a very different world. Can the Doctor see the truth before midnight arrives?

Battle rages across the skies as the Unholy Trinity unleash their deadly ambition. The Doctor, Belinda and Ruby have to risk everything in the quest to save one innocent life.