The novel opens with a young Russian woman of "progressive" sympathies, Varvara Suvorova, traveling to meet her fiancé Pyotr Yablokov, who has volunteered to fight in the war between Russia and the Ottoman Empire.

Varvara sees little of her fiancé, who is busy with his duties as an army cryptographer, so she spends her time at the correspondents' club, where she meets various interesting characters: Irish reporter Seamus McLaughlin, French reporter Charles Paladin, Romanian army liaison Colonel Lukan (unlike Bromfield's English translation, some others use proper Romanian spelling "Lucan"), Russian hussar officer Count Zurov (Fandorin's old friend from The Winter Queen), and the charismatic General Sobolev (based on the real-life Mikhail Skobelev).

In the end, Count Zurov breaks through to the Russian side, but after meeting the journalists at their observation outpost disappears on his way to the headquarters and Sobolev, out of ammunition, is forced to withdraw.

Pyotr unsuccessfully tries to hang himself, feeling responsibility for the carnage and defeat as he left the telegram unguarded when he went to welcome Varya and then sent it without checking; for the spy, knowing the not too strong Russian cipher, it was easy to replace it.

Varvara, on her way back from the hospital where she had been sent due to a case of typhus, encounters McLaughlin, the Irish reporter, who informs her that he has been tipped off that the Turks will surrender that night in a distant sector.

Thanks to his last-minute warning to Sobolev, the Russians manage to repel the attack after a fierce fight, the Turks in Plevna surrender, and McLaughlin, who has disappeared, is assumed to be the spy.

They believe him to have acted under direct orders of the British government, which – while ostensibly neutral – is in fact determined to prevent Russia from gaining a decisive victory over the Turks.

Fandorin is dispatched to London to track down McLaughlin and either kidnap him, bribe him to change sides by the promise of a Russian estate, or at least denounce and discredit him in British public opinion.

She has very mixed feelings about this proposal, but before she has time to respond the train arrives in San Stefano and Sobolev must give his full attention to securing control of the town.

Inside the vault, Anwar tells Varvara that after Sobolev entering Constantinople, the British fleet off the coast would open fire and Western powers would have declared war to Russia, bringing ruin to it.

His purpose is to defend the development of human rights, reason, tolerance and nonviolent progress in the Western world against the expansion of the despotic and barbaric Russian Empire.

His fatherland Turkey, which he deeply loves, is nevertheless the chess piece that he has planned to sacrifice or at least risk in his gambit in order to achieve a greater purpose – namely, to "protect humanity from the Russian threat".

Varvara and Pyotr board the train back to Russia, and Fandorin is there to say goodbye before he leaves by ship for a diplomatic post in Japan – farthest possible from home, the only thing he asked when offered a reward.

The novel ends with a newspaper article proving Fandorin right; the European great powers – in particular, Britain – object to the treaty and agree to a diplomatic conference to draft a new settlement much less favorable to Russia.