In a crowded nightclub, a well-known drug pusher is enjoying an evening out with several female companions. One of his junkie henchmen approaches him and tells him that he's driving the pusher's car, and he's brought him a young woman who is willing to do
anything to get some drugs. The pusher is angry until
he sees the person in the car, a beautiful woman who
returns with him to a shabby apartment. Just when it
seems like they are going to have sex, the woman pulls
a severely sawed-off shotgun out of her macrame purse
and blasts the dealer's head off. The henchman, who
is in the other room shooting up, is confronted by the
woman, who tells him her last name is Coffin, and that
her sister is LuBelle Coffin. LuBelle is now in a
hospital, having shot up with tainted heroin, and her
mind is permanently damaged. The enraged woman forces
the man to take another hit of heroin, which kills
him.
The woman is known to her friends and associates as
Coffy, a nurse at a city hospital. Coffy has a romance with political hopeful Howard Brunswick (Booker Bradshaw), but she is devoted to caring for her sister. She gets news of her "hit" from Carter (William Elliott), a policeman friend of hers. Carter is a good cop who refuses to take payoffs from local mobster Arturo Vitroni (Allan Arbus), and as a result, Vitroni sends his henchmen to knock Carter around. Coffy happens to be in the way at the time, and both of them wind up in the hospital. Coffy is little more than shaken, but Carter is beaten unconscious and seriously injured.
More angry than ever, Coffy sets out to stop the mobsters once and for all. She learns of a pusher named King George (Robert DoQui) who is supplying heroin to local dealers. George is also a well-known pimp; Coffy is vaguely familiar with George because one of his prostitutes, Priscilla (Carol Locatell), once came to Coffy's hospital after George cut her face. Coffy visits Priscilla at her home and leans on her for information about George and his business practices. Priscilla tells Coffy about Arturo Vitroni and how he is one of George's best clients. Vitroni apparently likes to treat his hookers cruelly, humiliating them and making them do degrading things for his pleasure. Priscilla balks when Coffy asks her where George keeps his stash; she is afraid that if she tells Coffy this, George will kill her, so she pulls a knife on Coffy and tries to frighten her off. Instead, Coffy turns violent, shattering a wine bottle and threatening Priscilla with the jagged edge. Priscilla tells Coffy that George keeps his heroin stash in a box under his fireplace. Just then, Priscilla's tough lesbian pimp, Harriet, returns and fights with Coffy, who just barely escapes.
With the information she got from Priscilla, Coffy is able to pose as a Jamaican hooker named Mystique, and she introduces herself to King George. George immediately takes her into his fold, much to the chagrin of George's 'old lady', Meg (Linda Haynes). During a party at George's pad, Meg dumps a tray of cocktails in Coffy's lap. Coffy sees her opportunity and she slips into George's bedroom to swap his heroin with sugar. She then picks a fight with Meg and winds up fending off Meg and the rest of the girls. Coffy emerges the victor when Meg cuts herself on a series of razorblades that Coffy has hidden in her afro. Arturo Vitroni witnesses the fight, and he so taken by Coffy that he requests a session with her the next night.
Coffy arrives at Vitroni's house and attempts to assassinate him, but she is stopped by Omar (Sid Haig), Arturo's bodyguard. They make the mistake of believing that King George has sent Coffy to make a hit on Arturo, so they retaliate. Keeping Coffy locked up, they lure George into a limousine and then kill him by tying a rope around him and dragging him behind the vehicle.
They are undecided about what to do with Coffy. Believing her to be a hit woman, the gangsters summon one of their financiers to question him about whether he is associated with Coffy's attempted hit. The financier turns out to be none other than Coffy's boyfriend, Howard. Vitroni is suspicious when he realizes that Coffy and Howard know one another, but Howard betrays Coffy and tells Vitroni that for all he cares, they can kill her.
Omar and some other goons take Coffy to a desolate area of the city with intentions of killing her and dumping the body. Along the way they inject her with some heroin they took from King George's stash--Coffy knows it's really just sugar. She distracts them with her feminine wiles and manages to stab Omar in the throat, mortally wounding him. Another goon chases Coffy out onto a busy freeway, where he is run down by a passing vehicle. The third goon, a crooked cop, dies when he tries to run Coffy down; she shatters his windshield with a brick and he flips the car.
Coffy returns to Vitroni's with her shotgun; she drives her car straight into the house, killing one goon who was standing on the porch. Inside she lets loose with her shotgun, killing everyone she sees until she has Vitroni cornered in a swimming pool. She toys with him and tells him she'll take a million dollar payoff to let him live, then she shoots him anyway.
Coffy's revenge isn't complete until she pays a visit to Howard. She slips into his house and surprises him, holding a shotgun on him. Howard is shocked to see Coffy alive, and even more shocked to hear that she's killed all of his shady associates. Howard manages to sooth Coffy, convincing her that he was only playing along to buy time. But his speech is interrupted by a woman calling for him from upstairs; a semi-nude white woman walks out of one of the bedrooms. Coffy responds by gunning down Howard right there in his living room, as the terrified woman screams in horror. Coffy then stumbles out into the morning light, grimy and covered with bloody scratches and bruises, but alive.