4 ideas
Thirteen human embryos were found in a Wanderers' sarcophagus and raised as ordinary people. Each was linked to a coded disk, a possible 'detonator', stored in the Museum of Extraterrestrial Cultures. When one of them, Progressor Lev Abalkin, secretly returned to Earth and went to the museum reaching for his disk, COMCON-2 chief Rudolf Sikorski shot him dead, and the novel never reveals whether Abalkin was a programmed agent or an innocent man.
Sikorski reasons that when the possible harm is civilizational and the evidence cannot settle the question, even a small chance that Abalkin is a programmed agent weighs heavily against one possibly innocent life. He reads evidence that might clear Abalkin as equally consistent with programming. Still, he acts only when Abalkin's own movements, his secret return and his approach to the museum and the disk, seem to bring the feared trigger within reach.
In the title image, a beetle placed in an anthill tests the ants, not the beetle. The foreign object's purpose may be to provoke and measure the colony's response. Applied to the foundlings, this means the Wanderers' real probe may be how humanity treats beings it suspects, so the defensive reaction itself becomes the data or the damage.
Abalkin was never told what he was, and he was blocked from his chosen life and watched. Because he did not know the reasons, his confused, evasive attempts to understand what was being done to him looked like an agent activating. Kammerer was also sent to hunt him without being told why, so the agency's information control produced both the anomalous signals and the investigator's inability to interpret them.