The McClanes take an injured Yuri Komarov to the location he has hidden the key to the "secret evidence" that the Russians and the CIA are after, and also to pick up his daughter. Big John has a hunch that something is off … and then the bad guys show up unannounced, and Yuri's daughter pulls a gun on her old man.
The bad guys take Yuri and the key away, and the McClanes are about to be executed, when Jack cuts through his cuffs and they fight their way free. The Russian dancer is beaten up but gets away into an armoured chopper. They turn their guns on the building, forcing the boys to jump out a window, and then a thousand feet down a vertical construction rubbish funnel.
John rallies his son to finish the game and go after the bad guy. They follow them to Chernobyl to help retrieve the evidence before it falls into the wrong hands.
At Chernobyl, Yuri and his team don anti-radiation suits and enter the bank. Yuri points to a safety deposit box, and the bad dudes drill the outer steel door open, then use the key device to open it. Suddenly the whole wall gives away to a chamber that hasn't been opened since the radiation leak - full of nuclear material. The burn away the ambient radiation (can you do that???) and enter, removing the suits.
Yuri at this point turns on the dancer, kills him, is reunited with his daughter who was bluffing all along, and suddenly the bad guys are somehow on the same side all of a sudden. Yuri makes a call to a masseur who dispatches his old enemy in mother Russia.
The McClanes show up, and gun down a few snipers. They find Yuri, who pretends to be his weaker alter-ego, but they aren't buying it. Yuri assumes he'll be taken prisoner, but instead Jack throws him from the roof of the bank, in a slight homage to Die Hard (part 1). Yuri's daughter goes bananas and turns the armoured chopper onto the bank.
John manages to get onto the chopper, but is locked out of the cockpit. He gets into a truck inside, ties it up with a few chains, then drives it off the ramp. The weight throws around the chopper and Yuri's daughter can't control it. John manages to jump out next to his son. The daughter, on a suicide mission, flies it straight towards them, but misses badly. The boys jump, again, to safety.
The McClanes have saved the day again, and at this point John Senior wisely passes the mantle down to John Junior.