Ohio, 1995 – Young Natasha Romanoff (Ever Anderson) plays with her surrogate sister Yelena Belova (Violet McGraw) until Yelena scrapes her knee. They go to their “mother” Melina Vostokoff (Rachel Weisz), who tends to the wound. Later, “father” Alexei Shostakov (David Harbour) comes home and tells Melina they have to leave. They take the girls to a hangar where they prepare to board a plane before a team of SHIELD agents pursue them. Alexei shoots at them while Melina tries to get the plane moving. She is shot, so Natasha must move up and take the controls while Alexei hangs on the wing. They manage to get the agents to crash all over the place before flying out of there.
The four arrive in Cuba, where Melina is given medical attention as Alexei meets with a man named Dreykov (Ray Winstone). When the nearby soldiers try to get the girls, Natasha swipes a gun off one soldier to defend Yelena. The men note that the girl has guts, and both girls are tranquilized and taken away in a truck.
A montage follows showing Natasha and Yelena, plus dozens of other kidnapped girls being taken to the Red Room, where they are subjected to harsh procedures and training through their lives, shaping them into powerful Black Widow agents.
21 years later, Natasha (now played by Scarlett Johansson) is on the run after violating the Sokovia Accords. General Thaddeus “Thunderbolt” Ross (William Hurt) and his men close in on the building where she is located. Ross attempts to talk to Natasha, but she makes it clear she is not going quietly. She manages to escape before Ross can catch up to her.
In Morocco, Yelena (now played by Florence Pugh) has her eyes on a target, Oksana (Michelle Lee). Yelena is spotted, and she pursues Oksana on foot. The two fight until Yelena fatally stabs Oksana in the gut. She then sprays Yelena in the face with a synthetic red gas called Red Dust that appears to break Yelena free from mind control. She realizes she just killed a close friend of hers. Yelena recovers the rest of the gas and removes a tracker from her body. Dreykov is informed of this when Yelena’s signal is lost, and he goes to dispatch his super-assassin, Taskmaster.
Natasha moves to a safe house in Norway where she meets her contact, Rick Mason (O-T Fagbenle), who supplies her with items like passports or whatever she needs. She is also sent a mysterious package. Later that night, Natasha runs out of fuel and goes to get more, only for Taskmaster to ambush her on the bridge. Natasha tries to fight the assassin, but Taskmaster is capable of mimicking moves and is quick to defend themself. Taskmaster attempts to grab Natasha’s package, but she already grabbed it before Taskmaster throws her off the bridge. Natasha finds that it is Red Dust, along with pictures of her and Yelena as children.
Natasha travels to Budapest to find Yelena in her own safe house. The two engage in a fight until they call a truce before they literally strangle each other. Yelena tells Natasha about the Red Dust and its effects, and she also lets her know that the Red Room is still active, despite Natasha having believed it to be destroyed when she supposedly killed Dreykov. Yelena mentions Dreykov’s daughter, just before several Black Widows come after them. The two run out of the building and topple a tower as Natasha has to shake one Widow off as she falls to the ground. When Natasha gets down to the Widow, she tells Natasha that Dreykov is forcing her to do this, just before Dreykov has the Widow kill herself.
Just as Natasha and Yelena try to escape, Taskmaster appears and pursues them through the streets. They steal a car and drive as fast as they can, but Taskmaster fires an explosive arrow that sends the car rolling down into the subway. Natasha and Yelena run, with Taskmaster following a trail of blood from Yelena’s arm, but the two managed to divert Taskmaster’s path as they hide. As Yelena tends to her arm, she brings up how Natasha believed that she killed Dreykov at the cost of his daughter Antonia’s life when trying to work for SHIELD. She was keeping watch outside his office when Antonia entered the building. When asked by an agent if they were clear to execute Dreykov, Natasha said yes despite Antonia being there, and the building blew up, killing her. This has haunted Natasha ever since.
Natasha and Yelena grab some supplies and get drinks while reminiscing about the past, with Yelena talking about the fake family they had and the training they went through. They know that, in order to bring down Dreykov and the Red Room for good, they need help. Natasha contacts Rick again, and he procures a plane for her and Yelena.
Alexei has been in prison, arm wrestling other inmates while regaling them with stories about how he was the Red Guardian, Russia’s first and only super-soldier. He tells the others that he battled Captain America, although another inmate believes it to be a lie, and Alexei breaks his hand for it. The alarms go off as Natasha and Yelena fly in over the facility. Alexei uses his super strength to break out of the building, but the guards go after him and try to attack the plane. Natasha descends and engages in combat with the guards while Yelena fires a grenade at a tower. This causes an avalanche that buries the facility, but Natasha is able to grab Alexei in time. However, both she and Yelena aren’t particularly happy to see them since he and Melina lied to them as kids. When they ask Alexei if he knows where to find Dreykov, he tells them that Melina might have an idea.
The three make a rough landing near a farm where Melina is using mind control on pigs. She reunites with her former fake family, and Alexei openly flirts with her (which grosses out Natasha and Yelena). He even goes to try on his old Red Guardian outfit, but he struggles to get it on due to gaining weight. While sitting at the table, things get tense as Natasha says that nothing from their past was real. Yelena is brought to tears, as she believed their family to be real.
Later, Melina tells Natasha that her birth mother was relentlessly searching for her until Dreykov had her killed. At the same time, Alexei tries to continue being a father figure to Yelena, although she is still too angry at him until he sings “American Pie”, which was her favorite song when they lived in Ohio. Moments later, Dreykov’s agents arrive, having been contacted by Melina. They subdue Natasha, Yelena, and Alexei before being taken away.
The group arrives at the Red Room, which is located in an aerial base for the utmost discretion. Melina is brought to Dreykov, although it turns out to be Natasha wearing a disguise. This was part of a plan she staged with Melina back at the house, with Melina taking Natasha’s place in the prison cell since she knows how to open the doors to free herself and Alexei. Yelena nearly has her head cut open until Melina talks to her via an earpiece to inform her of a blade she can use to free herself. Meanwhile, Dreykov reveals several things to Natasha. First, he has protected himself with a pheromone that prevents anyone from attacking him. Then he brings out Taskmaster, who is revealed to be Antonia (Olga Kurylenko), having survived the explosion with facial disfigurement, and her father has her mind-controlled into being the perfect super-soldier. He then shows Natasha the files of all the girls around the world that he has mind-controlled.
When confronted by guards, Melina blows up one of the engines on the Red Room, sending several guards falling, but also causing the whole facility to begin tumbling toward the ground. Alexei fights Antonia while Yelena and Melina battle the guards until Melina helps Alexei trap Antonia in one of the cells. Natasha then smashes her face against Dreykov’s desk to break her nose to block out the pheromone per Melina’s advice, allowing her to attack Dreykov. He brings in other Widows to attack Natasha as he makes his getaway, but Yelena sends the Red Dust to the room, blowing it up and breaking the Widows from their mind control. Natasha tells them to go free, and she stops to release Antonia from her cell, despite acknowledging that she will go after her. The Red Room starts to come apart even more, prompting everyone to make it outside to escape. Alexei and Melina make their escape, unable to wait for Natasha and Yelena. Dreykov and his guards board their getaway craft, but Yelena takes electric batons and jams them into the turbine, causing the ship to explode and blow up Dreykov and the guards. Yelena is thrown from the impact, but Natasha jumps and reaches her in time to give her a parachute.
Antonia catches up to Natasha and fights her when they land on the ground. Natasha opens her helmet and sprays her with the Red Dust, freeing her from her father’s control. Natasha is met by Yelena, Alexei, Melina, and the other Widows, who take Antonia in for recovery. Natasha bids farewell to her former family as Ross and his team start making their way toward the location.
Two weeks later, Natasha now has blonde hair and meets up with Rick again as he has gotten her a jet. She is set to help break out the other Avengers from prison and reunite with her second family.
Post-Credits Scene: It is now 2024. Yelena goes with her new dog to Natasha’s grave, following her sacrifice in “Endgame”. As she mourns her sister, she is met by Contessa Valentina Allegra de Fontaine (Julia Louis-Dreyfus), who now has Yelena under her employment. She gives Yelena a file on her next target, the one apparently responsible for Natasha’s death: Hawkeye.
