Aleksandra Ivanova, who goes by Sasha, is a young woman disguised as a male soldier named Aleksander Lipovsky in the Russian military. Approximately four years earlier, her wealthy, prominent family was massacred. Sasha survived only because her cousins shielded her with their bodies. Her Uncle Albert, the family mediator, survived along with his four-year-old son, Mike, and the family's grandmother, Babushka. Sasha's older brother, Anton, disappeared during the attack, and his body was never found. Two years later, mercenaries nearly killed Sasha, prompting Uncle Albert to fake her death and help her assume a male identity. She binds her chest, takes testosterone, and enlists under a false name, determined to uncover who ordered the massacre.
At the training camp, a fellow soldier named Matvey corners Sasha and attempts to pull down her pants, which would expose her female anatomy and destroy her cover. A captain from a visiting special operations unit intervenes. Sasha follows the captain and asks him to train her. He dismisses her as unfit but tells her to prove herself, cryptically suggesting she see if she can "take a man's place."
The captain is Kirill Morozov, a special ops leader haunted by his father's abuse. He encounters Sasha training alone at night and pushes her past her limits until she faints. He suspects she is a woman but chooses not to expose her. Viktor, Kirill's lifelong bodyguard, relays that Kirill's father, Roman Morozov, is demanding Kirill return to the United States, where the Morozov family holds a powerful position in the Bratva, the Russian organized crime syndicate. Kirill refuses.
Sasha's endurance improves dramatically, and Kirill selects her for his special ops unit. She befriends Maksim, a cheerful soldier who grew up in the Morozov household, and Yuri, a quieter strategist. When Roman visits the base, Sasha recognizes him as the man who came to her family's home days before the massacre. Filled with rage, she nearly stabs him but aborts when his armed guards appear. She is deeply conflicted to learn her captain is the son of the man she believes destroyed her family.
The unit deploys to clear an insurgent warehouse, but the mission is a trap. The warehouse explodes, killing the team leader and most of his men. Sasha provides sniper support from a tree but is shot in the upper back after deliberately exposing herself so Kirill can eliminate an enemy sniper. With communications destroyed, Kirill carries her through snow for over an hour. He removes her chest bindings, dresses her as a woman, and presents her to villagers as his wife, claiming she was shot by soldiers. An elderly retired doctor, Nicholas, and his wife, Nadia, treat Sasha's wound. When she regains consciousness, Kirill tells her he has known she was a woman since the day they met. She reveals her real name: Aleksandra. A snowstorm traps them for days, and physical tension builds between them. Armed men then attack the village, killing Nadia and Nicholas. Kirill forces a grief-stricken Sasha to flee, and Viktor eventually picks them up.
Maksim and Yuri suspect Roman sabotaged the mission to force Kirill home. Kirill announces he is returning to New York and offers his men the choice to stay or follow; every man chooses to go. Sasha tells Uncle Albert about Roman, but her uncle reacts with alarm, ordering her to stay away from all Morozovs and refusing to explain Roman's role. Despite his warnings, Sasha resolves to follow Kirill. He warns her that outside the military, her life will belong to him and obedience will be absolute. She agrees.
At the Morozov mansion in New York, Kirill faces a hostile family. His mother, Yulia, tells him to leave, and his younger brother, Konstantin, declares himself the new leader. Kirill visits his bedridden, dying father, who begs him to take over. Kirill tells Roman he will lead but destroy everything Roman built, then holds the oxygen mask away from Roman's face and watches him die. Karina, Kirill's younger sister, attacks him with a kitchen knife. Sasha disarms her. Karina has severe anxiety and agoraphobia resulting from a traumatic childhood ordeal Roman orchestrated.
To claim Roman's Bratva position, Kirill must secure approval from the Pakhan (supreme leader), Sergei Sokolov, and other key figures. Inside the family, Yulia and Konstantin vote against him. Sasha privately persuades Karina to vote for Kirill, deadlocking the family vote. Kirill then stages Yulia's kidnapping before the leadership meeting, arriving late and presenting himself as the devoted son who rescued his mother while Konstantin ignored the distress signal. The performance wins him a unanimous vote.
Kirill assigns Sasha as his night guard, and their physical tension escalates. She repeatedly tries to access Kirill's locked office for Roman's files about her family but finds all documents protected by Kirill's thumbprint. Kirill engineers a private encounter in the sauna, and they become physically intimate for the first time. When Rai Sokolov, the Pakhan's grandniece, nearly catches them at Kirill's nightclub, Kirill lets Rai believe he is gay rather than reveal Sasha's gender, negotiating silence in exchange for a future political favor. After Rai leaves, Sasha cries, worried about the political consequences for Kirill. He wipes her tears and kisses her for the first time.
Their power struggle intensifies when Kirill overhears Sasha speaking on a burner phone to Uncle Albert. She shoots the phone out of his hand to destroy the number rather than let him identify her contacts. Their confrontation is interrupted when Konstantin is beaten and dumped at the club. Sasha defies Kirill by caring for Konstantin and bringing Karina to visit him. That night, Kirill and Sasha have sex for the first time; he is rough and possessive, and only realizes afterward that she was a virgin. Their sexual relationship becomes a daily fixture, though Sasha privately tells herself they are only using each other. Kirill never sleeps beside her, always retreating to the sofa.
Over the following month, Kirill consolidates power by securing two cartel partnerships no one in the Bratva had managed before. Sasha bonds with Karina and learns that when Karina was 13, Roman dropped all three children on an isolated island as a survival test, during which Kirill was beaten and tortured trying to save his sister while Konstantin escaped with Yulia's help. One night, Sasha sings Kirill a Russian lullaby. He falls into a deep sleep for two hours, the first in roughly 20 years, and is disturbed by how completely he let his guard down.
When Uncle Albert reports that Babushka is seriously ill, Sasha requests three days off. On the drive to the airport, Kirill asks her three times not to go, the final time softly and pleadingly. She promises to return. In Russia, Sasha follows Uncle Albert's coordinates to an isolated warehouse, where her uncle appears in combat gear with masked mercenaries. He tells her she "did so well," puts a mask on her, and says he is proud. A snowmobile approaches, and Sasha recognizes the rider as Kirill, who followed her alone. Uncle Albert declares that Kirill was the mastermind behind the family's massacre and opens fire. The novel is the first book of the Monster Trilogy and ends on this cliffhanger, with the story continuing in the sequel, Lies of My Monster.