On the Metro, in the aging tunnels near Park Kultury, a section built in 1935 is already showing dangerous signs of structural strain. One tunnel night crawler, Sergeitch Sergey Sosnovsky, notices water seeping into the tunnel that runs beneath the Moscow River and informs the assistant station master, who brushes off the concern and jokes that it’s only groundwater. Meanwhile, Irina Garina Svetlana Khodchenkova is torn between her lover, businessman Vladislav Konstantinov Anatoliy Belyy, and her husband, surgeon Andrei Garin Sergey Puskepalis. Konstantinov tries to pressure Irina to divorce Andrei, setting the stage for a love triangle that will collide with catastrophe. Arriving from abroad, Irina spends the night with Konstantinov rather than going home, while Andrei must escort their daughter Ksenia Garin Anfisa Vistingauzen to school, though a misstep leads them to take the “Garden” station by coincidence.
As the day unfolds, Sergeitch shares a drink with Galina Elena Panova by the Garden, recalling that the water leaking into the tunnel carried a faint, slime-tinged scent that cannot be groundwater. The police detain them for drinking in public, but Galina slips away and escapes into the subway, leaving Sergeitch to plead for a phone to warn the dispatcher—only to be ignored. In the tunnel, water pours from the ceiling as a train bearing Garin, Konstantinov, and Galina arrives and the driver hits the emergency brake. The train derails, plowing into water and debris; several passengers lose their lives. Konstantinov crawls onto the car roof to survive, while Garin searches for Ksenia among the wreckage, and Konstantinov warns him that the conductor rail remains live. The water level climbs, a short circuit cuts power, and those who stay in the flooded zone die.
Garin, Konstantinov, Galina, courier Michael Stanislav Duzhnikov, and a pair, Denis Istomin Aleksey Bardukov and Alisa Katerina Shpitsa, scramble toward a passage leading to a maintenance shaft. Michael, terrified, hesitates at the exit and dies when the carriage rolls over. From the passage, they drop into a small, abandoned bunker built during the subway’s construction; above them, a vertical shaft ends in a sewer grate they cannot reach, and their mobile phones are useless underwater. As the water rises higher, tension grows between Garin and Konstantinov, who resents Garin’s questions about his relationship with Irina. When they finally manage to call Irina, they only manage to tell her that they are trapped in the bunker; they press against the bars of the shaft, hoping for rescue, but the flood’s pressure tears off the train head and the water level drops again, pulling the survivors back into the tunnel.
The survivors reach the ghost station Borodino near the Garden and regain their strength on the platform. Garin drops hints to Konstantinov that he suspects the two lovers’ involvement, and the two men clash, with Konstantinov nearly drowning again. In the flooded tunnel, the overhead arch collapses and water fills the space; the rescue team manages to shut off the water tap, but the group eventually returns to the bunker and makes it out onto the street through the bars. Alisa and Denis leave the hospital together, while Garin and Irina confront each other in a tense moment, with Garin implicitly shutting Irina’s appeals down. The film closes with Konstantinov driving in circles after the ambulance carrying Garin, leaving the future of the relationships unresolved and underscoring a city that keeps moving even as lives are forever altered by a sudden, catastrophic flood.
