In 1963 Mississippi, a twelve-year-old African-American girl is gang-raped by Ku Klux Klansmen. Relocated to Brooklyn, NY immediately afterward, Cassandra Monroe she sets her sights on revenge. Her trainer and mentor is Dante, a former Green Beret who teaches martial arts at a local community center. After eight years of intensive training, having grown into a strikingly beautiful assassin, she returns to Mississippi and kills her three rapists.

Shortly afterward, she’s assaulted one late night on a dark Brooklyn street. Upon subduing her assailant, she experiences an unfamiliar sense of exhilaration, even sexual arousal. Soon, late-night “hunting expeditions” for would-be predators become a frequent activity.

Meanwhile, Mike Borelli, a police detective from Bensonhurst, Brooklyn’s “Little Italy” section, who has resisted the corruption that plagues his precinct, is lured into a trap by his partner, and shot. Offered a partial disability pension to go away and keep his mouth shut, he accepts. An old high school buddy suggests that Mike join him in the Gambino crime family. He declines that, but does accept an offer to join them in a weekly poker game, hosted by Sammy “The Bull” Gravano. Mike starts a new life as a private eye.

On one of her hunting expeditions, Cassie is suddenly surrounded by three ruffians, stumbling out of a Bensonhurst bar. She dispatches two of them with chops and kicks, but the third pulls a gun. Mike appears from out of nowhere and knocks the gunman unconscious. Cassie’s reaction is not gratitude, but fury. In her mind, he has interrupted her mission, and she accuses him of “ruining everything.” Having just stepped into her life, Mike watches her stomp out of his. He is bewitched though, and without a clue yet as to why.

But Cassie’s closest friend, Amy, whom she’d rescued from a sexual assault, has a mystery to solve. Her big sister was the first victim of the Yellow-Tulip Killer, a serial murderer still at large. Amy insists on hiring Mike to work with them to bring the killer to justice. Using skill, stealth and luck, the team identifies the killer, Ronald Caldwell, and finds the incriminating evidence in his house. The problem is that they found it through illegal means. Mike had hired a local thief, Frankie “Batts,” to pick the front door lock for them.

While Mike strategizes on persuading the police to reopen this cold case, the women take matters into their own hands. They lure the killer into the wooded area where his eight victims were found. Cassie sends Amy away, then beats him to death and plants clues that will lead police to the evidence. Afterward, she lures Mike to her place for violence-fueled sex. When he finds out what she’s done, he’s horrified. But, still, he can’t stop thinking about her.

Cassie’s plan works. The police search Caldwell’s house and find the evidence. The Daily News reports a “grisly end to the Yellow-Tulip murders.” When Frankie Batts sees the address in the article, he concludes that Mike must have been Caldwell’s killer and spreads the word around Bensonhurst. This makes Mike a minor local celebrity. During poker night, Sammy the Bull invites him to join his mafia crew. Mike is afraid to turn him down, so he says he’ll think about it. Sammy accepts that, but warns, “Think long, think wrong.” Mike returns to the game, wondering if that was a threat.

Mike’s mother comes up from Florida for a visit. He learns, for the first time, that she’d been regularly beaten by his alcoholic father, until he left when Mike was five. Vague memories return. He wonders if her abuse, buried deep inside his subconscious, had something to do with Cassie’s magnetic pull on him. “Mom couldn’t fight back,” he thinks, “but Cassie does.” He begins to see her in a new light.

Mike invites Cassie to dinner at Romano’s, a fine neighborhood restaurant. She not only lets him through her hard shell, but opens up about her rape and the aftermath. During their meal, Mike notices dirty looks coming their way from other diners, who had never before seen a Black person at Romano’s. When he drives Cassie home, she invites him in. They spend the night together.

Mike’s office is ransacked early the next morning. During the week, he is tailed and shot at. He wonders whether this is a warning from Sammy the Bull. But the timing suggests it could be retaliation for bringing Cassie to Romano’s. He breaks off contact with Cassie until he gets to the bottom of it, to keep her out of harm’s way. She assumes he’s hiding an affair with another woman. One morning, she sees him leaving his house with a client, a glamorous redhead. The closer she gets to him, the hotter her jealousy flares. Equally hot are their reconciliations, which last only until the next misunderstanding arises.

Frankie Batts gets arrested in an attempted robbery. To get the charges reduced, he tells the police Mike had hired him to break into Caldwell’s house two days before he was killed. From this information, the police theorize that Mike might have not only killed Caldwell, but also planted the incriminating evidence, and was himself the real Yellow-Tulip Killer. To keep them away from Cassie, he again cuts off contact. This stokes her fury. She concludes he’s nothing but a no-good liar, who “got his taste for white meat back.”

Amy intervenes at the crisis point, while Mike is on the verge of being framed for murder, and after Cassie has gone off on a violent, self-destructive rampage. Once Cassie understands what’s really going on, she insists on putting herself forward as Mike’s alibi. He reluctantly agrees, and the case against him begins to fall apart.

Cassie’s campaign becomes more purposeful now. She becomes a champion of endangered women. Mike acts as her backup and lookout, as she prowls the night streets on predator patrols. While their love blossoms in the face of dangerous neighborhood racial hostility, they deal together with wife-beaters, actual and would-be rapists, Mike’s Mafia associates, the crooked cops he once worked with, Amy’s kidnapper, a pedophile priest, and even another serial killer. The remedies they apply are extra-legal at best, but effective.

On their first night living together, Mike realizes that, having fallen in love with an Avenging Angel, he’s bought into Cassie’s unusual moral code. His final thought that night is, “Heaven help us both.”