The TARDIS has landed in a war zone. The Doctor, Romana and K9 find themselves traipsing through an inhospitable battlefield. Strange lights flicker in the sky, and stranger creatures lurk in the darkness.
When rescued from an attack by a Sontaran tank, the time-travellers discover they're facing a far more dangerous foe than the battle-hungry clones. This terrifying fight has been going on longer than anyone can remember... and shows no signs of stopping.
With the TARDIS missing and their luck running thin, the Doctor and his friends' only hope of survival is to uncover the truth about what is happening on this planet. If they can discover the secret of the eternal battle they might just survive... but it might just mean the end of them all.