The color of space

A kidnapped scientist awakens aboard a vast rotating disc whose commander explains that a newly created helium-fluoride compound negates gravity, enabling enormous machines to seize famous buildings from Earth and threaten global stability. The captor outlines the ships' solar-reflecting boilers, gas jets produced by the compound's decomposition, and centrifugal artificial gravity, and offers the scientist return in exchange for his secret. Observing stars, Earth and the moon sweep past the window, the scientist confronts the moral and geopolitical implications as the machines plan to deposit the stolen monuments on Venus, forcing him to weigh loyalty against survival.