NOTE: This spoiler was submitted by Jeremy
John Wick (Keanu Reeves) crashes an SUV into a wall. He staggers on out of the vehicle, bloody and wounded. He puts pressure on a stab wound in his gut. As he crawls to the side, he takes out his phone and watches a video of his wife Helen (Briget Moynahan) on the beach. John slumps over and shuts his eyes.
Mere days ago, John woke up on a cloudy day. He has flashbacks to him being with Helen, up until recently when she collapsed in his arms. She had an illness that eventually claimed her life. It is the day of her funeral. After the service, John's old friend Marcus (Willem Dafoe) approaches him to offer his condolences.
That night, a delivery arrives for John. It's a small beagle. John finds a note from Helen. She wrote to him that she has made peace with her death, and now she wants John to find his. John weeps. He takes the dog out and looks at its collar, which has a flower on it, leading John to figure out Helen named the dog Daisy.
Daisy follows John on his day as he takes his Mustang out. He stops to get gas at the same time as three Russian mobsters, including Iosef Tarasov (Alfie Allen), son of mob boss Viggo Tarasov (Michael Nyqvist). Iosef comes up to John's car and compliments it, and then asks how much he wants for it. John says it's not for sale. Iosef then goes over to Daisy, but John scares him away. One of Iosef's buddies peeks his head into the car and wishes John a good day.
As John is getting into bed, Daisy needs to use the bathroom. When they get downstairs, there are two men in shadows standing before John, while a third takes a bat and whacks John in the head. He starts beating on John while Daisy whines. One of the men goes over to the dog and breaks her neck. The man pulls off his mask to reveal Iosef, who knocks John out. John later wakes up and goes over to Daisy, stroking her head.
Iosef takes John's car to a shop run by Aurelio (John Leguizamo). Aurelio immediately recognizes the car and demands to know where Iosef got it. Iosef brags about who he stole the car from and that he killed this person's dog. Aurelio slugs Iosef in the face. Later, John comes by the shop and asks if Iosef came by, and Aurelio gives John his name to confirm that's who took his car and killed his dog. Even later that night, Viggo calls Aurelio to ask why he struck Iosef. Aurelio says because he stole John Wick's car and killed his dog. Viggo simply replies, "Oh."
John takes a sledgehammer into the basement and begins smashing the floor open. He uncovers a stash of guns and bullets.
Viggo meets with Iosef in his home to discuss the situation. He socks his son twice in the stomach to reprimand him, reminding him who he just committed a crime against. Viggo tells Iosef that John was associated with him once, until he met Helen and decided to leave. John apparently had a reputation as "The Boogeyman", or rather, the guy they called to kill the Boogeyman. Viggo calls John up to try and resolve the matter, but John hangs up on him.
Viggo sends a team of masked hitmen to John's home to kill him. However, John gets the drop on them and takes them all out with ease. He shoots them down and ends up fighting the last few before stabbing the last guy through the heart. John then calls a clean-up crew to dispose of the bodies. This is not the first time they have done business with John, and they know it won't be the last.
Viggo meets with Marcus and asks him to kill John Wick for a new contract that he's put out worth $2 million. He also instructs his assistant Avi (Dean Winters) to call for others to take the job. Marcus accepts.
John goes to a hotel, the Continental, to stay as he conducts his business. There, he sees a woman he recognizes, known as Perkins (Adrianne Palicki). John meets another old friend, Winston (Ian McShane), over trying to find Iosef.
At night, Marcus gets to the roof of the building across the street and prepares his rifle to aim into John's room. From the mirror, he sees someone entering. He fires a shot to warn John. It's Perkins. She starts shooting at John while he tries to dodge her. She tells him that Viggo has doubled the contract if she breaks the rules of the hotel. He eventually gets Perkins in a headlock and offers her mercy if she tells him where to find Iosef. She tells John that he's in the bathhouse downstairs in the hotel. John then knocks Perkins out and leaves her with his associate Harry (Clarke Peters).
John goes into the club/bathhouse where Iosef and his buddies are. As soon as they spot John, he begins shooting at them while Iosef runs away. John kills every hitman in his path, but he loses Iosef as he flees in a getaway car.
Harry keeps Perkins cuffed to a chair, unaware that she has dislocated her thumb to slip out. She gets out and puts a pillow over Harry's face before shooting him.
John goes to a church where Viggo keeps his secret stash of money. After shooting the other goons in the church, John forces the priest to guide him to where the money is. He lights it all on fire.
Viggo learns of the fire moments before he is caught in a hail of gunfire courtesy of John. Although he kills most of Viggo's men, he is knocked out when an SUV rams into another, throwing John off his feet. Viggo captures him and wonders why he's gone to great lengths for revenge.
John tells him that the dog was a gift from his dying wife, and that Iosef took that from him. Viggo leaves him with his henchmen for them to suffocate him with a plastic bag. However, Marcus is watching from the next building, and he shoots one hitman in the head to let John take out the other. John gets his gun and shoots at Viggo's getaway car, leaving only him alive. Viggo is forced to tell John that Iosef is hiding in a safe house in Brooklyn.
The safe house is guarded by armed men, but none of that stops John from killing them and storming the place. Iosef once again tries to make a run for it, but John catches him and finishes him off.
In retaliation for Iosef's death, Viggo has his goons find Marcus and bring him to Viggo's home. There, they beat him good until Viggo and Perkins shoot him to death. Viggo calls John to tell him this, just before boarding a chopper out of there.
Before going to the chopper, Perkins is cornered by four men led by Winston, who tells her she broke the rules of the Continental. The four men execute her.
John finds Marcus's body and sets off to take Viggo down. He finds the villains heading to the chopper and tries ramming into them with his car. Viggo makes Avi go out and kill John, only for John to ram into him with his car. Viggo tries to push John's car over the edge, but John gets out safely. The two then fight hand-to-hand in the rain. VIggo tries to stab John, but John pushes the blade into himself before grabbing it and sticking it in Viggo's neck. He leaves him to die.
We go back to the first scene where John is still bleeding. After watching the video with Helen, he is inspired to keep on going. He goes into a dog shelter and tends to his stab wound. He then takes a dog with him, and they go home together.