Yuichi Kimura, "The Father", boards a bullet train in Tokyo in search of the attacker of his son Wataru. 

Meanwhile, guided by his handler Maria Beetle, operative "Ladybug" is assigned to retrieve a briefcase full of cash from the same train.

Also on the train are two English assassin brothers codenamed "Lemon" and "Tangerine" who were given the job to take care of the briefcase and the white death’s son.

Who just rescued a man ("The Son") from kidnappers and are taking him and the briefcase to his father, a Russian-born Yakuza boss called "The White Death".

During the trip, The Son is killed by poisoning. Which makes it more alert to Lemon and Tangerine. Ladybug discreetly steals the briefcase.

On his way off the train, is attacked by another assassin, codenamed "The Wolf", who recognizes Ladybug from his wedding, where his wife was killed.

Yuichi finds the person who attacked Wataru, a young woman codenamed "The Prince", but she overpowers him.

She explains that she pushed Wataru off a roof to lure Yuichi to the train as part of a plan to have him kill his boss: the White Death.

To ensure his cooperation, she has a henchman holding Wataru hostage in the hospital. If he tries to kill then the henchman will kill his son.

Ladybug, recognizing Lemon from a job in Johannesburg gone wrong, offers to return the case in exchange for being allowed to leave.

Lemon suspects that Ladybug killed The Son, leading to a fight. Lemon is knocked unconscious during the fight, and privately discusses Ladybug's innocence to Tangerine

The Prince finds the briefcase, booby-traps it with explosives, and rigs Yuichi's gun to explode if fired.

Ladybug encounters Tangerine, and after avoiding the White Death's men, kicks Tangerine off the train as the train departs, who manages to climb back aboard from outside.

Suspicious of the two, Lemon shoots Yuichi but collapses after drinking from a water bottle Ladybug had previously spiked with sleeping powder.

The Prince shoots Lemon and conceals him and Yuichi in a bathroom. Ladybug encounters "The Hornet", who poisoned both the Wolf's wedding party and the Son with the venom of a boomslang snake.

 After a struggle, both are exposed to the venom, but only Ladybug receives an anti-venom that saves him.

Tangerine runs into the Prince and notices one of Lemon's train stickers on her, realizing that she shot Lemon. Ladybug interrupts them, and Tangerine is killed before he can shoot the Prince.

At the next stop, Yuichi's father, "The Elder", boards the train. He recognizes the Prince and informs her that Wataru is safe, as the henchman has been killed by his guard.

After she flees, the Elder tells Ladybug he will remain to confront the White Death, who killed his wife while taking over the Yakuza.

Finding Yuichi and Lemon still alive, the four work together to make preparations to face the White Death. 

 At Kyoto, Ladybug gives the White Death the briefcase. The Prince, revealed to be the White Death's daughter, fails to goad him into shooting her with the rigged gun. 

The White Death explains that everyone on the train was linked to the death of his wife. He hired them hoping they would kill each other.

The White Death's henchmen open the briefcase, which explodes, knocking Ladybug and the White Death back onto the train. The White fights with the Elder.

The train crashes into downtown Kyoto. Emerging from the wreck, impaled with the Elder's katana, the White Death tries to kill Ladybug, but the Prince's rigged gun explodes in his face. 

The Prince threatens Ladybug, Yuichi, and the Elder with a machine gun but is run over by a tangerine truck driven by Lemon, who fell off the train earlier.

Maria arrives to retrieve Ladybug, while Japanese authorities begin to clean up the damage caused by the train crash.