The
War
Games
What a story! The War Games, at ten episodes, is a marathon epic of Dr. Who viewing. At the time of its broadcast in 1969 it was the second longest Dr. Who story and remains to this day arguably the second longest.
I think the idea behind The War Games is one of the best concepts ever introduced into Doctor Who. The notion of a race of aliens kidnapping soldiers from the Earth and putting them in similar surroundings on another planet to fight is highly original.
I find that I can watch The War Games over and over again without losing interest. It is a superb story telling how the Doctor is first able to cross through the barriers between different war zones and then finally infiltrate the central control area to discover the Aliens' plans.
At the end of story, the Doctor is put on trial for breaking the laws of time. He is spared, although not without punishment, and is exiled to Earth and forced to regenerate.
I presume that Jon Pertwee must have been cast at the time the final episode of The War Games was recorded although he does not appear. Thus the Troughton/Pertwee changeover is the only regeneration in Dr. Who history which we do not see on-screen.