In their search to the final segment to the Key To Time, the Doctor and Romana land on war-torn Atrios, which has been fighting a war of attrition against its twin Zeos. As there's variable radiation counts even 140 meters beneath the surface, one can imagine what it's like on the surface. The Doctor jokingly says of the high radiation reading that it might not necessarily be nuclear war, that someone might be holding a huge breakfast party.
Things begin bad, as usual. The Marshall, the military leader conducting the war, mistakes the Doctor and Romana as Zeon spies, yet he does a volte-face and welcomes the Doctor as "the one to head us to victory." However, he's not all he seems. One, he makes his decisions by meditating and mumbling in front of a black reflective surface. Two, he has a tiny black object around his neck. Three, he and Princess Astra, a figurehead in charge of people's morale and comfort, are at odds what with her pacifist stance.
Astra and her lover, the surgeon Merak, are trying to contact Zeos to try to negotiate a peace, but something is jamming their communications. The same jamming that is blocking the navigation system of the Marshall's fleet, perhaps? First Astra, then the TARDIS, and then the Doctor vanishes, kidnapped by sinister masked figures in black robes. On Zeos, he meets his nemesis the Shadow, who's working for the Black Guardian in the same way the Doctor's working for the White Guardian.
The Doctor's condemnation of a war fought by machines is given when he describes the commandant of the Zeon side as a "passionless lump of mineral and circuitry, highly efficient, doing very well, giving Atrios a beating, killing millions without a flicker, just doing it's job, and it's totally invincible.