When two Boston police officers are brutally murdered on the same day that Spenser (Mark Wahlberg), a former cop, is released from prison, he partners with his tough new roommate, Hawk (Winston Duke), to delve into the investigation and bring the culprits to justice. The intricate plot thickens as Spenser grapples with his past, haunted by the memory of a murder he couldn’t prevent, particularly the death of police captain John Boylan ([Michael Gaston]), who he suspects was involved in shady dealings during a murder investigation five years prior—an encounter that left Spenser incarcerated. Many of the characters surrounding him harbor resentment, both from his time in prison and due to the police corruption that runs rampant.
Set against the backdrop of South Boston, the film explores themes of greed spurred by rising real estate prices and the controversial casino project on the site of the former Wonderland dog track. Spenser’s fierce determination leads him to expose corrupt officers with the help of Hawk and their elderly boxing mentor, Henry (Alan Arkin). Alongside them are comedic interludes provided by Spenser's loyal dog, Pearl, and his ex-girlfriend Cissy (Iliza Shlesinger), who attempts to reenter his life in awkward ways.
After Henry picks up Spenser from jail, he introduces him to their shared living situation with Hawk, who is training under Henry for a boxing career. Despite Cissy's intent to reconnect during Spenser’s release, he avoids her, haunted by their past. That same night, Boylan meets a grim fate, murdered after being lured to a secluded location.
As events unfold, Driscoll (Bokeem Woodbine), the officer in charge of Boylan’s murder investigation, quickly places Spenser at the top of the suspect list. Following the day’s shocking events, another officer, Terrence Graham, is found dead in a car, ruled a suicide. Spenser, who held Terrence in high regard, begins to suspect that the police are covering up a deeper conspiracy.
In his quest for the truth, Spenser discovers evidence of drugs planted in Terrence’s apartment, a tactic used to exert control over his wife. Conversations with Terrence's partner suggest that Terrence was together with him during Boylan's murder, leading Spenser into a violent confrontation with corrupt officers. With Hawk’s help, Spenser views CCTV footage which hints that Terrence’s car was implicated in Boylan's murder without Terrence being present.
As the duo digs deeper, they unearth connections leading back to Bentwood ([James DuMont]), an ex-Irish Mob leader linked to the murder of an activist named Elise ([Cassie Ventura]), five years earlier. Spenser learns of Bentwood's threatening behavior towards Elise, culminating in her tragic demise—an unsettling story that a journalist tries to uncover further. When confronting Boylan in a drunken state, Spenser uncovers evidence of domestic abuse, leading to a violent clash that lands him back in prison.
While there, he recalls an assassination attempt on him, igniting his determination to find out who orchestrated it. After a tense interaction with Squeeb (Post Malone), a hitman from his past, Spenser learns of a connection to an old racetrack called “Wonderland,” a financial hotspot for a new casino project looming over Boston.
In a climactic turn, Spenser’s ongoing investigation leads to the ransacking of Terrence’s apartment, and his wife hands Spenser a wire containing damning evidence—a recording of Boylan revealing key details about the drug money flow and the behind-the-scenes machinations orchestrated by Driscoll, who had cut Boylan out of the Wonderland deal.
In a desperate bid for accountability, Spenser confronts Driscoll, but the corrupt officer remains unrepentant. With mounting pressure, Spenser resorts to seizing the drugs being funneled to corrupt officers, risking everything to expose the wrongdoing. The stakes escalate when Driscoll retaliates by kidnapping Henry, pushing Spenser to launch into action and confront the criminal elements head-on.
In a gripping showdown, Spenser defeats Driscoll and his associates, placing all captured evidence in plain sight before contacting the FBI, which ultimately clears Terrence of wrongdoing. In the end, Spenser’s relentless drive for justice prevails amid a web of deception and treachery.
