“Under the Rose” centers on the activities of Porpentine, a British spy in Egypt during the Fashoda crisis of 1898, when the British forces of General Kitchener encountered a French expeditionary troop in the contested area of the Sudan. The “Situation,” as it is referred to in the story, portends an international crisis that could lead to war in Europe, but the real focus of “Under the Rose” is on a small company of secret agents hoping either to promote or to prevent the final catastrophe.

Porpentine and his partner, Robin Goodfellow, are committed to preventing the “balloon” from “going up,” their phrase for the outbreak of an international catastrophe. They are opposed in their efforts by a group of agents, presumably German, who are equally committed to the eventual outbreak of war. The foreign agents are led by an old veteran spy named Moldwoerp and include his subordinate Lepsius and one other agent unfamiliar to the British. Porpentine soon deduces, though, that the other agent is actually one Hugh Bongo-Shaftsbury, supposedly an amateur British archaeologist.

Bongo-Shaftsbury has attached himself to the family of Sir Alastair Wren, who are on tour. In turn, Goodfellow has formed an attachment to Sir Alastair’s oldest daughter, Victoria. The entire company of tourists and spies embarks on the train for Cairo, and en route Goodfellow is nearly killed by an Arab hired by Lepsius. Bongo-Shaftsbury also manages to frighten Victoria’s young sister, Margaret, when he shows her an electrical throw switch stitched into his arm.

In Cairo, Porpentine observes Goodfellow and Victoria in bed together, although Goodfellow is apparently impotent. Despite this interlude, the British agents get to work. They believe that the foreign spies are planning to assassinate Lord Cromer, the British consul-general, hoping that the incident will precipitate the general crisis into all-out war. To try to force the diplomat to take precautions, the two stage several mock assassination attempts, but Cromer seems to take no notice of them.

Finally, Porpentine and Goodfellow follow the consul-general to an opera house where Manon Lescaut (1893) is being performed. There, the two find Moldwoerp and Lepsius arrayed and Bongo-Shaftsbury in the audience with a gun. Porpentine is tempted to shoot Lord Cromer and resolve the situation once and for all, but when confronted by Moldwoerp, he fires “perhaps at Bongo-Shaftsbury, perhaps at Lord Cromer. He could not see and would never be sure which one he had intended as target.”

Shoving aside Moldwoerp, whom he tells to “go away and die,” Porpentine rejoins Goodfellow. Despite Goodfellow’s misgivings, the two pick up Victoria and pursue the foreign agents into the desert, near the Great Sphinx of Gizeh. Porpentine, though, finds himself weaponless and outnumbered and is killed by Bongo-Shaftsbury for having insulted his chief. In the final paragraph of the story, the reader finds Goodfellow years later at Sarajevo, futilely hoping to prevent the rumored assassination of the Archduke Francis Ferdinand that will finally precipitate World War I.