When the Doctor, Jamie and Zoe arrive on Earth they find themselves in the midst of a terrifying battle. At the centre of the mystery stand aliens who have kidnapped soldiers from different periods of Earth's history and brainwashed them in to fighting each other. Their aim is to form an invincible army from the survivors and use this to take over the galaxy. When the Doctor learns the terrible purpose of the War Games he has one chance to defeat the aliens and end the Games... but to take it means risking recapture by his own people, the all-powerful Time Lords who are waiting to bring him to trial and who are capable of ending his very existence.