Plot summary

When two Boston police officers are murdered on the day that Spenser (Mark Wahlberg), an ex-cop, is released from prison, he teams up with his no-nonsense new roommate, Hawk (Winston Duke), to investigate and take down the guilty parties. The complexities of the plot revolve around Spenser's refusal to walk away from an unjust killing (one murder was of the police captain John Boylan (Michael Gaston) he himself suspected of malpractice (of suppressing a murder investigation) five years prior, and whom he attacked inside his home, landing him in jail). He is hated by many of the film's key characters - prison inmates and cops (mainly, corrupt ones).The film unfolds in South Boston, where rising property prices and a casino project on the former Wonderland dog track, fuel greed and police involvement in selling drugs to obtain a share of the project. Spenser takes down corrupt police, through determination and an odd alliance with ex-con Hawk and their elderly boxing trainer, Henry (Alan Arkin). His dog, Pearl and ex-girlfriend, Cissy (Iliza Shlesinger), provide comedic elements.Henry picks up Spenser from jail when he is released. Spenser is scared of Cissy and avoids her even though she comes to the jail to pick him up. Henry takes Spenser to his house, where Spenser realizes that he is sharing the room with Hawk, who is being trained by Henry for an upcoming boxing career. That same night Boylan is brutally murdered after receiving a phone call to be at a certain secluded spot at night.Driscoll (Bokeem Woodbine) is the investigating officer of Boylan's murder & tells Spenser that he is top of the suspect list. The same day Terrence Graham, another cop is found dead in his car, apparently a suicide. Police concludes that Terrence killed Boylan and then shot himself. Spenser knew Terrence from academy and knows that he was a good cop. He is not convinced. Spenser tracks Terrence's wife and finds that cops found narcotics in their apartment, which Spenser knows were planted and used to keep his wife under control. Spenser talks to Terrence's partner and finds that on the night of Boylan's murder, Terrence was in the cop bar with him. Spenser is beaten up by cops for showing up at the bar.Spenser looks at the CCTV footage from outside the bar (Hawk helps Spenser) and finds that Terrence's car was used the day before to ambush Boylan at the secluded spot and Terrence himself might not be there. At the murder scene, Spenser finds evidence that Driscoll was also there at the night of Boylan's brutal murder. Hawk and Spenser are having dinner when Hawk spots the corvette that Terrence left in the night Boylan was killed. Someone else drove Terrence's car to the ambush scene. Hawk notes the car plate. Spenser runs the plates and finds they belong ex Irish Mob boss Bentwood (James DuMont).Spenser knows that Bentwood was connected to the murder of an activist Elise (Cassie) 5 yrs ago. Bentwood was threatening Elise as he was a goon for hire. Elise was found murdered in the trunk of her car. A journalist showed Spenser a video of goons attacking Elise and killing her (which he claims was share with the police), but he and the journalist are not able to figure out what Boylan (who was the chief of police) was hiding. Spenser goes to Boylan's house, finds him drunk, and evidence of domestic violence, and ends up hitting him badly and gets 5 years in prison. Spenser remembers that there was an assassination attempt on him on his last day in prison. He meets Squeeb (Austin Post) who was part of the hit squad and demands to know who ordered the hit on him. Squeeb only says "wonderland". Wonderland is an old racetrack, which is being demolished to erect a new casino just outside of Boston.Just then Terrence's apartment is ransacked and his wife calls Spenser. She hands over a wire, which has Terrence's last recording. The recording reveals Boylan telling Terrence that the Wonderland deal was organized by Driscoll, who was trying to cut Boylan out of the deal. Boylan reveals to Terrence how the money transfer to the cops was taking place, which is why both of them were killed by Driscoll. Spenser meets Driscoll and gives him one last chance to come clean. Driscoll refuses. Spenser meets the FBI, but they say that Spenser does not have enough evidence against Driscoll. At his wits end, Spenser kidnaps the drugs which was fueling the payment to the cops, which they were using to buy their share into wonderland.Driscoll kidnaps Henry. Spenser attacks, defeats Driscoll and his men, places all the drugs and the evidence in open view and calls the FBI to hand over everything. Terrence is cleared of wrongdoing.