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, replacing a sick colleague, Carver. Ladybug is reluctant, as his recent string of bad luck during his jobs resulted in accidental deaths. Also on the train are two English assassin brothers codenamed "Lemon" and "Tangerine", 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. Ladybug discreetly steals the briefcase, but 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. The Wolf mistakenly believes Ladybug to be one of her killers. Ladybug confusedly fights The Wolf, who accidentally kills himself with a deflected knife throw. 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.

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 (due to him having left him unconscious instead of killing him), before both split off to find Ladybug and frame him for the Son's murder. 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 yet another assassin, "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, not knowing Carver (his wife's killer) was replaced by Ladybug. The White Death's henchmen open the briefcase, which explodes, knocking Ladybug and the White Death back onto the train. The White Death's remaining henchmen board and battle the assassins, while the Elder duels the White Death.

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 fruit 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.

At Tokyo Station, Yuichi Kimura, a former hitman, boards the "Hayate" train on the Tōhoku Shinkansen bound for Morioka to take revenge against the teenage Satoshi Oji, who is referred to as "the Prince" by his friends. Kimura's six-year-old son, Wataru, is in a coma after the Prince pushed him off the roof of an apartment building for fun. However, the Prince knows exactly who Kimura is and actually lured him onto the train. When Kimura approaches, the Prince knocks him out with an improvised taser and ties him up. The confident Prince is a sociopath who likes to manipulate people, and when Kimura awakes, the Prince takes control of him, threatening Wataru's life; an acquaintance is watching over him in the hospital and will kill him if the Prince is harmed and unable to answer his phone.

Tangerine and Lemon are an odd couple of skillful hitmen; Tangerine is composed and well-read, while Lemon is frantic and obsessed with Thomas & Friends. The pair just rescued the kidnapped son of mob boss Yoshio Minegishi, and they are returning the boy and suitcase of ransom money to Minegishi in Morioka. Lemon misplaces the suitcase, and Minegishi's son mysteriously ends up dead while they leave him unattended. At each station on the way, Minegishi's subordinates are also assigned to check on their progress, so Tangerine tries to think of a way out.

Nanao is a hitman with the code name "Ladybug", who constantly laments how unlucky he is; every job he takes has been successful, but somewhere it goes wrong and becomes much more difficult than anticipated. His handler Maria has procured him the easiest job she could: to board the Shinkansen at Tokyo Station, steal the suitcase from Tangerine and Lemon, and immediately get off at Ueno Station. When he tries to get off in Ueno, he comes face to face with "the Wolf", another hitman with a vendetta against Ladybug, who is about to board the same train car. Recognizing Ladybug, the Wolf doesn't let him off and brags about his luck taking on a new contract and meeting Ladybug at the same time. Ladybug gets the upper hand in a brief struggle and unintentionally breaks the Wolf's neck when the train rocks. Meanwhile, the Prince comes by to use the restroom and notices something is odd as Ladybug holds up the Wolf, awkwardly calling him a drunk friend, and tries to shoo the Prince away. Ladybug hides the Wolf's corpse in a seat, takes the photo of the Wolf's target, and hides the suitcase in a hidden compartment in the trash receptacle while he finds a seat to wait for the next station, where Maria tells him to get off. When the Prince returns, he discovers the hidden suitcase and tries to think of ways to further manipulate other passengers for his entertainment.

Each of the three sets of hitmen escapes from their own crisis, and the prince takes action on the immobile Shinkansen to play with the adults.

Stage

Maria Beetle was adapted as a stage play in Japan in February 2018.[15][16]

Film

The novel also inspired the Hollywood film adaptation, Bullet Train, directed by David Leitch and starring Brad Pitt. The film was released theatrically on August 5, 2022.[17]