Deimos, moon of Mars — where Lord Slaadek's plans to revive the ancient Ice Warrior civilization hang by a thread. Only the Doctor can stop him… but an old enemy, hiding in the catacombs, has an alternative plan, one that will test the Doctor's heroism to its limits. Just how far will the Doctor go to prevent the destruction and resurrection of Mars — on a day when his friends become enemies, and his enemies have right on their side?