Iosef, this heir to a crime family, had taken a fancy to John Wick's '69 Mustang at a gas station. He wanted to buy it, but John wasn't selling.
The next day, Iosef broke into John Wick's place when he wasn't home. He stole the car and killed the puppy that had been barking.
Iosef didn't know who he had provoked. This idiot had even planned to beat up John Wick in passing.
John Wick had been fully retired for four years, and had always led a peaceful life since.
Who would have thought that all of a sudden, an idiot would break into his house one day, steal his car, and kill his dog.
Looking at the surveillance footage, John could see who had stolen his car and killed his dog.
This car was one of his few possessions.
That dog was his last gift from his dead wife.
John Wick didn't hesitate. He wanted to kill this guy.