In a lush, sun-drenched state preserve in Palm Glade, Florida, a young couple in a parked car wakes from a night of drunken carousing to find the body of a headless woman submerged in the area known as Fisheating Creek.
Meanwhile, Jim Longworth, a detective with the Florida Department of Law Enforcement, is about to break 80 in a golf game against Carlos Sanchez, his medical examiner, when he gets word of the body from his partner, Mike Ogletree. Ogletree believes the woman's death may be connected to a spray-painted message, "Okeechobee Southerners Are Sub-Human," which has been popping up all over town.
Longworth breaks from his game (but not before cordoning off the area as a crime scene to preserve his winning streak) and heads back to the station. Once there, he learns that his partner has interviewed Erin and Justin, the teenage couple who found the body, and sent Justin home. He theorizes that whoever killed the woman did so elsewhere, dumping the body in Fisheating Creek so that an alligator could destroy the evidence.
Later that afternoon, Longworth investigates the crime scene, poking at the murky creek with his nine iron, and gets bitten by an alligator in the process. He ends up at the hospital where he meets and attempts to flirt with Callie, a tough, pretty health care worker who dresses his wound, but seems to have no interest in anything more.
At the station again, Longworth and Ogletree go over the case and run tests on the victim. Then, looking for a woman's perspective on the evidence he's gathered, Longworth meets Callie outside the hospital and woos into her a date to discuss the case.
Once again on the beat, Longworth interviews Justin and learns that Erin, the girl he was with that night at the creek, is actually his deceased brother's girlfriend. As it turns out, Justin's brother was killed on his motorcycle by a tourist from Maine, an obvious sore spot for the teen.
Longworth goes looking for Sanchez at the neighborhood bar after discovering that he neglected to inform him of an alligator tooth found in the dead woman's body. At the bar, he finds Ogletree drinking Bourbon and lamenting an earlier fight with his wife, but before they can talk Ogletree is gone.
On his date, Longworth questions Callie about her thoughts on the evidence and she agrees that if the victim was a tourist with children, someone would be trying to get ahold of her by now. Later on the porch, Callie and Longworth drink and Longworth opens up about his past, explaining that he collected a bit of money from the state after his captain shot him (mistakenly assuming that Longworth had slept with his wife) and used it to move to Palm Glade. Callie also introduces Longworth to her young son Jeff, who seems to find the detective mildly amusing.
Longworth brings medical assistant Daniel Green to the state preserve in search of the alligator whose tooth was found in the murdered woman. Spotting the gator, Longworth shoots it dead and later has the animal autopsied by Sanchez. During the autopsy, the murdered woman's jaw bone is discovered inside the reptile.
Longworth takes this information back to Ogletree, who throws his hands up at the whole thing and insists Longworth gather more information before trying to obtain dental records for the recovered jaw. Besides finding the jaw bone, Longworth explains he's gone to the local high school and discovered more information about the motorcycle accident that killed Justin's brother, a boy named Lane. He produces a yearbook with Lane's school picture, above a quote that reads "Okeechobee Southerners Are Sub-Human," the same quote which has been tagged all over town in recent weeks, suggesting that the anniversary of Lane's death has not been forgotten by Justin.
Longworth finds Justin at a restaurant in town and hypothesizes that he might've killed the victim, a tourist, in order to avenge his brother's death. He also asks Ogletree to check with the high school to see if any of the teachers are missing (since Lane's quote had been scrawled ominously over the walls there) but his partner rebuffs at the idea of being told how to do his job.
At the creek, Longworth once again searches for clues. He finds shoe prints in the mud, along with a receipt from a local convenience store. When he follows the receipt to the store, he spots Callie's son Jeff hanging out there and smoking with older kids.
Callie reapplies Longworth's bandages at the hospital and he offers to take Jeff out for the day so she can get some work done. He also phones his partner, who tells him a substitute teacher at the school has recently gone missing. Ogletree expects some kudos from Longworth on his discovery, but Longsworth has already hung up the phone, too caught up in the case to care.
On State Road 301, Longworth pulls off the road to pay his respects at a makeshift shrine for Lane and finds Lane's former girlfriend, Erin, already there. They talk about loss and Longworth questions her about the disappearance of the substitute teacher who once gave her detention for writing "Okeechobee Southerners Are Sub-Human" on an assignment, suggesting perhaps she too was involved in the headless woman's murder.
Jeff joins Longworth out at the creek as he searches for clues. While there, Longworth gets a call from Ogletree who has located the missing substitute teacher and determined she'd simply ran off with a guy for the weekend.
Longworth joins Ogletree at his house for a barbeque and presses him to reveal what's been eating him the past few days. Ogletree expresses frustration over the fact that he is treated like a secretary despite being Longworth's superior. Longworth apologizes, acknowledging Ogletree is under a lot of stress because of all the fighting with his wife.
Ogletree lets on that he knows Longworth searched his wife's dental records and is incredulous about being investigated by his own partner. Longworth explains Ogletree's shoe prints (from state-issued police shoes) and the deceased woman's profile which perfectly matched his "missing" wife were what made him suspicious and ultimately gave him away.
From a quick summary of the facts, its clear Ogletree murdered his wife because she was leaving him. Olgetree finally confesses to the crime and blames Longworth for causing him to loose all his confidence. He asks his partner to give him an hour so he doesn't have to shoot him, but it is too little too late, as the uniformed cops swarm onto the scene to arrest him.
Back on the golf course, Longworth and Sanchez finish their game, ruminating over the facts of Ogletree's crime. Just shy of the final hole and riding on his 80 stroke win, Longworth picks up his golf ball as a symbolic end to the game, but Sanchez insists he actually take the final shot.
At dinner, Callie chastises Longworth for ending the game with an 81 as they enjoy a quiet night together, finally having a chance to get to know each other.