The Drop by Dennis Lehane

Bob tends bar at his cousin Marv's establishment in the Flats. The bar is no longer owned by Marv, but by the Chechen mafia. A robbery at the bar one evening gets a cop named Torres involved in the doings at the bar and the unsolved case of Richie Whalen, who went missing after leaving the bar ten years earlier. Bob also draws attention when he takes in a pit bull that's been abused. Bob decides to keep the dog even though the owner, Eric Deeds, a local criminal, makes it clear that he wants the dog back. The Drop tells the story of Bob, Marv, Torres, and Eric as their lives intersect.