This book and the pre-war novel Over My Dead Body both involve international intrigue over Montenegro, but under very different circumstances, first concerning Nazi designs on the Balkans, and later in the context of Josip Broz Tito's Yugoslavia.

It may be only a coincidence, but it's natural for a trained detective —In The Black Mountain, Nero Wolfe's oldest friend and fellow Montenegrin Marko Vukcic is murdered by a Yugoslavian agent who has already made his escape from New York.

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.

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.

Wolfe gives a fake name and 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).

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.

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.

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 immediately.

Stritar produces a letter (a fake sent by Telesio as a red herring) which states that "Nero Wolfe" will be remaining in New York and sending funds to support the independence movement.