The novel takes place on a future Earth (vidphones, telepaths, androids, ionocraft are normal) recently conquered by aliens from Ganymede: limbless, worm-like creatures whose physical needs are attended to by a slave-race of specialist 'creeches'.

When the offer is violently declined, Mekkis sends Percy X and Joan to the Norwegian clinic of psychiatric genius Rudolph Balkani, who has had exceptional success turning resistors into enthusiastic collaborators via sensory deprivation therapy.

Meanwhile, the Neeg-parts have seized a cache of weapons developed by Rudolph Balkani during the war — machines that turn illusions thought up by their users into reality, and a 'hell-weapon' that was never used against the aliens, as it would destroy humanity as well.

After killing Percy X, Rivers is able to switch off the device before humanity is destroyed, but the Ganymedians instinctively form a group mind in times of danger, and so become trapped in a permanent existential and experiential 'hell' within a dark void, unable to contact their creeches for help.

The novel ends with the creeches returning to Ganymede to start their own society, and the World Psychiatric Association supporting Gus Swenesgard as a useful puppet ruler until democracy is restored, though Dr. Rivers can't help wondering as to their true motives.