Nathaniel, an art gallery owner with a dislike of danger, accompanies his detective friend Freya to Heidi van Seegeren’s party. Their mutual art collector friend hosts celebrations for Solday, a holiday observed on Mercury in the city of Terminator. On this day, the sun’s rays are let through the city’s protective gate for all to enjoy. Mercury is the art capital of the solar system, and Freya is eager to see a Monet at the party when it is illuminated during the party. When Nathaniel and Freya arrive, they are waylaid by Heidi’s new secretary, Sandor Musgrave. Eventually, they are allowed into her home where they encounter members of the art community, including the famous art dealer Arnold Ohman who procured the Monet that interests Freya. Suddenly, as the party reaches its climax and the gates are opened, there are screams of murder. Sandor Musgrave is found dead, and Freya is enlisted by the police to solve the murder.

Musgrave is determined to be an unsavory sort and several party attendees are named suspects. The investigation drags until Nathaniel finds Freya running chemical analysis on the paints of the Monet. She has developed a theory that the Monet is actually a forgery, but cannot find the evidence in the painting’s chemical composition to prove it. She and Nathaniel discuss the potential ways to prove the forgery (such as with doctored Monet records and synthetic paints) but cannot arrive at any conclusion. Nathaniel suddenly exclaims that Musgrave had been pointing to Heidi’s patio before he died. The patio was constructed from the Dover cliffs, and Nathaniel insists that Musgrave was communicating that the original English owners were the forgers of the painting. Freya does not confirm his conclusion and instead arranges a meeting with Arnold Ohman. When he is late, she and Nathaniel discover that he has been strapped to the mechanism that propels the city around the planet. Arnold claims to not know who put him there, but as Freya dallies to rescue him, he admits that he believes the forger is responsible. As Freya delays further, he agrees to comply with her plans for dealing with the forger.

The next day, the partygoers and police reassemble at Heidi’s. Freya reveals that while each suspect had ample motive, none had the opportunity. All are shocked to learn that Musgrave died from being disoriented by the bright light and injuring himself. A few days later, Freya asks Nathaniel to accompany her to see someone off from Terminator’s transit station. The individual turns out to be Arnold, who Freya is exiling to Pluto. Freya reveals that Arnold is in fact the murderer and responsible for the Monet forgery as well as collections of fakes by other famous artists. She was able to corner him with the realization that Monet would have used natural chalk derived from the Dover cliffs--Arnold used natural chalk from a North American source. Her unconventional approach to solving crimes prompts her to send him to the edges of the solar system where she believes he will be able to practice his craft, enriching the world of art without having to masquerade under the names of the masters.