What is the plot of the movie John Wick?

John Wick is grieving the death of his wife, Helen, from an illness. To help him cope, she arranged for him to receive a beagle puppy. A few days later, John is accosted at a gas station outside of New York City by a group of Russian gangsters, led by Iosef, who fail to intimidate John into selling them his 1969 Boss 429 Mustang. That night, the men break into John's home and kill the puppy before stealing the car. Iosef takes the Mustang to a chop shop to remove its identifying details, but the shop owner, Aurelio, recognizes the vehicle and refuses service. John learns from Aurelio that Iosef is the son of Viggo Tarasov, the boss of the city's Russian mafia.

Learning of his son's actions, Viggo beats and berates Iosef for incurring John's wrath. Viggo reveals that John was formerly a hitman in his employ, renowned and feared in the criminal underworld as the "Baba Yaga," a ruthless and relentless "man of focus, commitment, and sheer will." After John fell in love with Helen, a civilian, Viggo gave him a seemingly "impossible task" to earn his freedom.

John recovers his concealed stash from his former career, including weapons and gold coins used as underworld currency for special services. He refuses Viggo's attempt to make amends for his son's actions and kills the hit squad subsequently sent to his home. As a result, Viggo puts a $2 million bounty on John's head, and his former mentor Marcus is enlisted to take him out. John lodges in the city at the Continental, a luxurious hotel that serves as neutral ground for the underworld and where conducting criminal "business" is strictly forbidden. The hotel's owner and John's old friend, Winston, secretly informs John that Iosef is at the Red Circle nightclub. John infiltrates the club and confronts Iosef, but he is attacked by Kirill, Viggo's henchman, and forced to retreat to the Continental for medical attention.

As John rests, he is targeted by a hitwoman named Ms. Perkins, who sneaks into his room. Marcus sees Perkins from an adjacent building and fires a warning shot to alert John. He wakes up and subdues Perkins, who reveals that Viggo doubled the bounty for her to kill him in the hotel. She also discloses that Viggo has a high-value stash concealed in a church. John has another hitman, Harry, secure Perkins, but she escapes and kills Harry.

At the church, John destroys Viggo's cache of cash and extensive blackmail material. When Viggo arrives to assess the damage, John assaults him and his men but is captured after being hit by Kirill's car. John tells Viggo that he will not stop until Iosef is dead because the puppy gave him hope and a chance to not be alone in his grief for Helen. Marcus intervenes again to save John, allowing him to kill Kirill and threaten Viggo into revealing his son's location. John assaults the safehouse and kills Iosef. Afterward, Marcus encourages John to return to the everyday life he has built, but their meeting is witnessed by Perkins, who reveals Marcus's duplicity to Viggo. He has Marcus tortured and killed before calling John to taunt him with the details, drawing him back to the city.

Perkins is executed at Winston's behest for breaking the Continental's rules, and Winston informs John that Viggo is preparing to leave the city by helicopter. John races to the New York Harbor, where he fights and mortally wounds Viggo. Resigned to dying from his own injuries, John watches a video on his phone of Helen telling him they need to go home. He breaks into a nearby animal clinic, treats his wounds, and adopts a pitbull puppy scheduled to be euthanized before beginning the walk home.