Doctor Who: The War Games

The Doctor, Jamie and Zoe arrive on an unnamed planet. At first believing themselves in the midst of World War I, they realise it to be one of many War Zones overseen by the War Lords, who have kidnapped large numbers of human soldiers in order to create an army to conquer the galaxy. Infiltrating the control base, the Doctor discovers that the War Chief is also a member of his own race. The creeping realisation sets in that the Doctor cannot solve this problem alone, and that his days of wandering may be at an end...