The four brothers are Jack (played by Mark Wahlberg), Bobby (played by Tyrese Gibson), Angel (played by Evan Ross), and Jeremiah (played by André Benjamin). They were all adopted by a caring woman named Evelyn Mercer (played by Fionnula Flanagan) who took them in as troubled youth.
When Evelyn is killed in a convenience store robbery, the brothers come back to Detroit to mourn their loss and pay their respects. However, they soon discover that her death was not just a random act of violence, but a targeted hit. They vow to find the killers who took the life of their mother figure and bring them to justice.
As they investigate, the brothers clash with a powerful and corrupt businessman named Victor Sweet (played by Chiatwetel Ejiofor), who they suspect is behind the murder. Along the way, they also encounter a police detective named Green (played by Terrence Howard), who is reluctantly helping them but warns them of the danger they are in.
The brothers use their street smarts and toughness to track down the people responsible for their mother's death. Along the way, they face numerous obstacles and challenges, but their bond as a family helps them persevere. In the end, they exact their revenge against the killers and find closure for their loss.