As Archie is about to leave the brownstone for a basketball game, Sergeant Purley Stebbins calls with news that Wolfe's old friend Marko Vukcic has been shot and killed. After Archie identifies the body, Wolfe joins him at the morgue and insists on being taken first to the crime scene and then Rusterman's Restaurant, owned by Marko.
Wolfe and Inspector Cramer question the employees there, and Wolfe and Archie return to the brownstone to find a surprise visitor: Wolfe's adopted daughter Carla. She and Marko have been involved in a movement to secure Montenegro's independence from Yugoslavia, and she is furious at Wolfe's refusal to support the effort. Wolfe tries to question her, but she is reluctant to give any information, since she believes that he may be in league with the government of Yugoslavia or the Soviet Union.
During the three weeks following the murder, Wolfe pursues various lines of investigation and gets a second visit from Carla, enraged that the police are now looking into the movement's background. Following this meeting, he gets three updates from Paolo Telesio, an informant in Bari, Italy. The first states that Carla has returned to Bari and crossed the Adriatic Sea into Montenegro; the second is a cryptic message on the killer's location - "the man you seek is within sight of the mountain"; the last states that Carla has been killed. Realizing that "the mountain" must be Lovćen in Montenegro, Wolfe makes immediate plans to go there and find Marko's killer, accompanied by Archie.
The two fly to Europe, making their way to Bari and taking temporary shelter in a house owned by one of Telesio's friends. Telesio arranges for a guide to ferry them across the Adriatic; from there, the two hike through the foothills of Lovćen and eventually secure a ride to Rijeka Crnojevića and then Podgorica. Jubé Bilic, a college student, drives them to Podgorica and drops them off at the office of Gospo Stritar, the local police chief. Wolfe passes himself off as a Montenegro native who has lived abroad for many years and is now returning to decide which side to support in the struggle over Yugoslavia's future, and Archie as his American-born son to explain his inability to speak Serbo-Croat.
Although Stritar is skeptical of Wolfe's explanation, he allows the two to go about their business, but dispatches Jubé to follow them. Wolfe and Archie travel to the home of Marko's nephew Danilo, who had passed the messages on to Telesio and who has been helping Marko and Carla smuggle weapons and supplies in from the United States. Danilo learns of Jubé's surveillance and has him killed, then reluctantly agrees to take Wolfe and Archie into the mountains for a meeting with Josip Pasic, one member of a guerrilla team in the independence movement. From Pasic, Wolfe learns that Carla had begun to suspect that a spy had infiltrated the group; she slipped into Albania to infiltrate a Russian-controlled fort and gather information, only to be killed instead.
Wolfe and Archie sneak into the fort, where they hear screams coming from one room. Inside, they discover Peter Zov, a man they had previously seen in Stritar's office, being tortured by three Russians. Their leader berates Zov for going to New York and killing Marko on Stritar's orders, hampering Russia's goal of taking over Yugoslavia if the Tito regime is overthrown. Carla had gained the favor of the other two Russians; when they realized who she was, they killed her.
Wolfe and Archie storm the room, and Archie kills the Russians and frees Zov. The gun he used to kill Marko is found elsewhere in the fort, and Wolfe makes up his mind to take him back to New York to face justice rather than exact revenge on the spot. Once the three have returned to Podgorica, Wolfe pretends to have decided to commit himself to the Tito regime and offers Stritar a large bribe in support of it. Stritar produces a letter (a fake sent by Telesio) which states that Wolfe will be remaining in New York and sending funds to support the independence movement. Zov is dispatched to assassinate him as an associate of Marko.
The three return to Italy, where Wolfe and Archie arrange a trans-Atlantic ship voyage under their assumed names and Zov comes aboard as a steward. Wolfe insists on having Zov brought to the brownstone so that he can reveal himself on the spot. When the ship pulls into the New York harbor, though, a news photographer spots Wolfe on the deck and calls his name. Zov draws his gun and shoots Wolfe, wounding him in the leg before being tackled by the rest of the staff. Satisfied that both murders can now be closed, Wolfe tells Archie to call Cramer.