The film opens with a funeral taking place in the small village of Tropoje, Albania. The funeral is attended by the Albanian mafia where several armed men stand over the graves of their fallen brothers. Their leader, Murad Krasniqi (Rade Serbedzija), tells them that they will have their revenge, and they will kill Bryan Mills (Liam Neeson).
The next scene takes place in Los Angeles where Bryan appears to be working at a car wash, but just wants to buff the car himself. He goes to the home of his ex-wife Lenore (Famke Janssen) to see their daughter Kim (Maggie Grace). Lenore tells Bryan she is with her boyfriend. Bryan is clearly not thrilled to hear that. He drives over to the boyfriend's house using a GPS he furtively put in Kim's phone. He interrupts their make-out session and has Kim leave so she can continue practicing driving (she is now 18 years old and failed her road test twice already). Kim is not happy that Bryan is still overprotective of her even after three years (since the events of the first film when she was kidnapped by Albanian human traffickers).
In Paris, France, the Albanians break into the home of Bryan's friend Jean-Claude and torture him for information on Bryan's whereabouts, but Jean-Claude has no idea. The villains will later discover that Bryan is headed to Istanbul, Turkey, on personal business.
The next day, Bryan goes to visit Lenore, only to find her crying because she has been fighting with Stuart, her husband, and as a result, he canceled their planned trip to China. Bryan suggests that she and Kim join him in Istanbul, but Lenore says she doesn't want to impose.
Meanwhile, the Albanians arrive in Istanbul via a mountain pass as they await Bryan's arrival. When he gets there, he stops at his hotel and makes a phone call to Lenore. He starts to leave a message, only to be surprised by her and Kim.
In his room, Bryan pulls out a trunk full of weapons. Kim and Lenore are staying in the next room. At night, Bryan and Kim take a ride on a boat on the Bostrophes, and Bryan not-so-subtly asks about her boyfriend Jamie (Luke Grimes). He asks if she loves him, but she doesn't know yet. She mentions how Lenore described her relationship with Bryan before having Kim as being "magical."
The next day, Bryan and Lenore allow Kim to go off and have fun while they take a ride through the area from a local taxi driver. However, during the ride, Bryan senses danger. He tells the driver to go a certain route and begins telling Lenore to go back to his hotel room to be safe. She gets out of the car and runs away while Bryan takes the car from the driver. He tries calling Kim, but she is swimming in the hotel pool and doesn't hear her phone. Lenore gets trapped and can't make it out. A few Albanian thugs corner Bryan and he immediately begins to beat them up. However, one of them brings Lenore captured. He orders Bryan to drop his gun. He then calls Kim back and informs her that he and her mother are about to be taken. She is scared, but he tells her where to go to be safe because he knows they'll look for her too. After he hangs up, he breaks the phone and they brutally assault him, and then capture him and Lenore.
Kim leaves the pool and heads to her room, then walks out the window to the next room where she hides in Bryan's closet before the other thugs come in to find her. Security guards notice them, but the thugs kill them.
At the villain's hideout, Bryan is tied by his wrists to a pipe. While he is alone, he takes out another hidden cellular phone and tries to call his friend Sam (Leland Orser) but gets no answer. He tries Kim again, and she tells him that she's safe. After she gets out of the closet, Bryan tells her to get a grenade and toss it out the window onto a parking garage and to let him hear the explosion so he knows how close she is and where she can find him. He is forced to hang up and hide the device as Murad comes in. Murad shows him pictures of the last film's villains, all of whom died at Bryan's hands. Murad pulls out a picture of Mirko, his son (the one Bryan killed by sticking him with the nails hooked to battery cables, electrocuting him until his heart burst). Bryan says he did what he did because they kidnapped his daughter, but Murad doesn't care. He still intends on making Bryan suffer. He brings in Lenore and cuts her neck, then hangs her upside down with a bag over her head to see how long it takes until the blood in her head is gone. He tells Bryan that once they capture Kim, Murad will personally kill her and force Bryan to watch before he personally kills Bryan.
Bryan manages to free himself and get Lenore down. He calls Kim again and continues telling her where to go by throwing more grenades. He senses she is close and keeps telling her where to go. He breaks a steam pipe and sends steam up a chimney, which he tells Kim to zero in on. Kim drops a gun down the chimney. He escapes from the hideout and starts killing more Albanians in a shootout. Meanwhile, Kim is roof-hopping and is eventually cornered by one thug, who gets shot by Bryan who has escaped. He embraces a terrified Kim and takes her away.
They steal a taxicab as Bryan tries to get Lenore back in less than five minutes, which he monitors by setting a timer on Kim's phone. He is too late, and the villains take Lenore away. He gets back to Kim, who is forced to drive the cab through the city away from the villains who give chase in their own cars. Bryan tells her to drive to the American Embassy, and they eventually outrun the villains and crash through a booth after getting shot at. Bryan manages to call Sam again and asks him to contact anyone who can protect them. He tells Kim that the villains are hunting him, and she will be safe in the embassy. He promises he will find her mother.
Bryan eventually finds where Murad and his goons have taken Lenore. He storms the complex and continues killing off the bad guys, even getting into a prolonged fistfight with one goon who almost stabs Bryan, but he takes him out quickly and grabs his gun. He finally corners Murad in a small room with the gun. Bryan asks him if he has other sons. Murad says he has two. Bryan knows if he kills Murad, they will seek revenge as well, so he opts to spare Murad's life because he is just tired of all the killing. He sets the gun down and starts to walk out. However, Murad grabs the gun and pulls the trigger as Bryan's back is turned, only to discover the gun is empty. Bryan hands him the bullet he took out, and then easily snaps Murad's neck, killing him. He goes over to Lenore, who is lying on the floor unconscious, but she comes to, and they embrace.
Three weeks later. Kim is taking her road test, and she passes. Bryan hugs her, and she invites him for a celebration. She takes him and Lenore to an ice cream parlor. The waitress brings four sundaes and in enters Kim's boyfriend Jamie. She asks Bryan if it's okay, and he appears not to be okay with it, but he lightens up and welcomes him to join them.