Second paragraph of third chapter:
But Craator could see exactly what they were.
To be honest, not one of the more memorable Sixth Doctor novels. The Doctor and Peri land in a crumbling authoritarian society, closely aligned with the setting of the Judge Dredd comics. Peri ends up with the rebels and the Doctor (after flirting with death) with the Adjudicators. Lots of running around and biffing. You can get it here.