Short Version:
Karla (Halle Berry) hunts down and kills all those responsible for the kidnapping of her young son, Frankie (Sage Correa), helping to bring down, at the same time, a nationwide child abduction ring.

Long Version:
Karla is a waitress and single mom to a young boy, Frankie. She is also embroiled in a messy custody battle with her ex-husband. One day, while spending an afternoon at a carnival with Frankie, she is forced to briefly turn away from the boy to answer a phone call from her divorce lawyer. She returns to find Frankie gone; while searching for him, she spots him being dragged into a car (a green 80s Mustang), to be driven away. She tries to stop the vehicle by clinging to it but it still runs off on her.

Karla decides to engage in a frantic, tense persecution of the vehicle, marred by multiple incidents: some woman tossing objects from the back of the Mustang to thwart her effort; another figure repeatedly threatening to kill Frankie if Karla doesn't back off; a cop who tries to first pull Karla over and then help her when she tips him off into the situation, only for him to be apparently killed by the abductors; the female kidnapper, whose name happens to be Margo (Chris McGinn) -Karla heard this on Frankie's toy recording device earlier-, forcing Karla to let her hop on Karla's minivan and, then, try to kill her, with Karla being able to fend her off; Karla going into a police station to report Frankie as missing, only to run off shortly after, realizing that she could lose her son unless immediate action is taken; the other abductor changing vehicles; and so on.

Eventually, the male abductor (Lew Temple) -whose name, Karla discovers, is Terrence Fickey- catches up with Karla and tries to kill her, but she causes her minivan to roll and crash backwards, which kills Terrence. By finding his licence, she learns where he lives and heads there on foot.

After wandering around the house and trying to call 911, Karla spots a barn where Frankie is being held in an attic, along with two other girls. Meanwhile, Margo returns, realizes Karla's presence and pursues her and Frankie to a nearby lake, where they hide under a pier. Margo finds them but, before shooting them, Karla drags her into the lake and strangles her with her flashlight, causing her to drown.

Karla then returns to the barn to help the two girls when in comes a bearded man (Christopher Berry), an alleged neighbour, who first holds Karla at gunpoint until she explains there are children imprisoned in the attic. He offers to help THE TWO GIRLS come down. Upon seeing this, Karla grabs a shovel (she never said there were TWO children up there nor that they were GIRLS); figuring out he is the mastermind of those kidnappings, she hits him with the shovel, killing him, while saying: "You took the wrong kid!!"

The Police finally arrive; Karla and all three kids are safe; the event becomes a big story in the media, as, in the aftermath, a massive child abduction ring has been dismantled, with multiple nationwide arrests being made, and Karla is hailed as a hero.

Thanks Julio!