4 ideas
After surgeon Professor Dowell dies, his assistant Professor Kern secretly keeps the severed head alive with Dowell's own perfusion technique and makes it direct further research, which Kern then publishes as his own. The secret comes out through Marie Laurent, a nurse hired to tend the head, and Dowell's son Arthur.
When a person depends completely on a keeper for air, speech, and stimulation, the keeper can extract their intellect without persuasion by granting or withholding those inputs. Kern needs Dowell's knowledge but not his consent, because he can mute him, deny him comfort, and threaten his survival. Dependency turns expertise into a resource the keeper can harvest.
The novel argues that intact thought cut off from a body is torment rather than a gift. Brigitte begs for a body because life as a head alone is unbearable to her.
Belyaev treats life-extension surgery as a question of who owns the revived person, not only of what is technically possible. He also has Marie committed to an asylum to keep his work secret, which shows secrecy about the work turning into abuse of the people around it.