| Director | Clint Eastwood |
|---|---|
| Budget | $25 million |
| Box office | $156.6 million |
In 1975, Irish-American neighborhood friends Jimmy Markum, Sean Devine, and Dave Boyle are playing street hockey in Charlestown, Boston. After the boys write their names in a patch of wet concrete on the sidewalk, two predators posing as police officers abduct Dave and rape him for four days until he escapes. One of the kidnappers dies before they can be caught, and the other is arrested and later dies by suicide in prison. 25 years later, Jimmy is an ex-convict and neighborhood convenience store owner; Sean is a detective with the Massachusetts State Police whose pregnant wife Lauren recently left him, and Dave is a blue-collar worker continually haunted by the abduction and rape he suffered. Jimmy and Dave are connected by marriage: Dave's wife Celeste and Jimmy's second wife Annabeth are cousins.
Jimmy's daughter from his first marriage, Katie, plans to run away to Las Vegas with Brendan Harris, a boy from a family Jimmy despises that she has been secretly dating. One night, Dave sees Katie and her friends at a local bar. That same night, she is murdered, and Dave comes home bloodied and injured, claiming he fought off a mugger and possibly killed him. Sean and his partner Whitey Powers investigate the murder while Jimmy, distraught at Katie's death, conducts a separate investigation using his neighborhood connections.
A witness statement suggests that Katie may have realized her killer. The detectives understand that the gun used to kill her, a .38 Special revolver, was also used in a liquor store robbery in 1984 by "Just Ray" Harris, Brendan's father. Harris has been missing since 1989, but Brendan claims he still sends his family $500 monthly and feigns ignorance about Ray's gun. Whitey suspects Dave, who keeps changing the story about how his hand got injured. Dave continues to behave erratically, which upsets Celeste to the point that she leaves their home and tells Jimmy she suspects Dave is Katie's murderer.
Jimmy and his friends invite Dave to a local bar, get him drunk and confront him when he is about to vomit. Jimmy admits to Dave that he killed "Just Ray" for implicating him in the liquor store robbery, which resulted in his imprisonment. Dave reveals to Jimmy that he did kill someone that night, but it wasn't Katie; he killed a child molester whom he found with a child who was being sex-trafficked. Jimmy, not believing him and after forcing him to admit to Katie's murder, kills him and disposes of his body in the adjacent Mystic River. Meanwhile, after finding his father's gun missing, Brendan confronts his mute younger brother "Silent Ray" and his friend John O'Shea about Katie's murder. He beats the two boys, before John pulls out Ray's gun and is about to shoot Brendan. Sean and Whitey, having connected the teens to the murder, arrive in time to disarm and arrest John and Ray.
The next morning, Sean tells Jimmy that John and Silent Ray confessed to killing Katie as part of a prank gone wrong. Sean asks Jimmy if he has seen Dave, who is wanted for questioning in the murder of a known child molester. Jimmy does not answer, instead thanking Sean for finding Katie's killers. Sean reunites with Lauren after apologizing for pushing her away, while Jimmy confesses what he's done to Annabeth. During a local parade, Sean sees Jimmy and points a finger gun at him, but Jimmy shrugs it off.