Las Noches de Diciembre (Spanish, "The Nights of December") is a small terrorist cell led by renegade newspaper columnist Skip Wiley, a brilliant-but-insane Uncle Duke-like character, as El Fuego . Wiley believes that the only way to save Florida's natural beauty from destruction is to violently dissuade tourists from visiting and/or settling in the state. Recruiting three comrades with similar axes to grind against the Florida establishment, they begin a spree of flashy kidnappings, murders, and bombings to frighten off new arrivals into the Sunshine State.
Fittingly, their first victim is B.D. "Sparky" Harper, the head of the Greater Miami Chamber of Commerce. Harper's body is found stuffed into an oversized suitcase, dressed in a garish tourist outfit and smeared with suntan oil, and with his legs amputated. Next, Wiley's gang starts kidnapping and murdering random tourists and Florida residents, many of whom are fed to a giant North American Crocodile (nicknamed "Pavlov").
Brian Keyes, a private investigator and former news reporter for the Miami Sun , is hired by the Public Defender's office to help defend the police's prime suspect in Sparky Harper's murder, a petty burglar named Ernesto Cabal, who was caught driving Harper's stolen car. Brian is inclined to believe that Harper's murder is much too bizarre to be Ernesto's work, but the Miami police, in their eagerness to close the case, dismiss him. Ernesto commits suicide when his own lawyer states that the case is a lost cause.
Brian is then hired by Nell Bellamy (the wife of the first tourist victim) to find her missing husband, and by his old mentor, Sun editor Cab Mulcahy, to locate Wiley, who has disappeared.
After an uncomfortable encounter with Wiley's girlfriend, Jenna (Brian's ex-girlfriend), Keyes tracks Wiley to a cabin in the Everglades, where he is abducted by Las Noches . Wiley reveals himself as the group's leader, and tells Brian that his job is to return to Miami (alive), and spread the word of Las Noches demands. But Wiley also says that he is not ready to have his own role exposed yet, and warns Brian that if he does so, then the violence will escalate, immediately and horribly. To drive home the fact that Las Noches is serious, Wiley has Keyes witness as their latest victim, retiree Ida Kimmelman, is fed to Pavlov. Keyes tries to stop the murder, and is stabbed in the back by one of the gang, a Cuban named Jesús Bernal. Keyes is returned to the city and treated in the hospital.
Since it is the start of the tourist season, the police's initial reaction to Keyes's warnings is to cover up, dismissing the Las Noches communiques as a hoax. Sun reporter Ricky Bloodworth uncovers the letters and writes an article on the letters, but misspells the name of the group, as "Las Nachos ". The terrorists retaliate by triggering several bombs in public places, forcing the authorities to take them seriously. Keyes's old friend, Detective Al Garcia is appointed head of a task force to catch the terrorists.
Based on Wiley's hints, Keyes, Mulcahy, and Garcia deduce that the terrorists plan to kidnap Miami's much-touted Orange Bowl Queen, in the most spectacularly public fashion possible. Since the civic leaders flatly refuse to cancel the Orange Bowl Parade, or to allow police guards to be seen near the beauty queen, Garcia suggests hiring Keyes as her undercover bodyguard.
Keyes is pleasantly surprised when the recently crowned beauty queen, Kara Lynn Shivers (19), turns out to be an intelligent, self-possessed, and thoroughly sensible person. She actually hates the whole beauty queen "racket," and takes part only to indulge her father's fanatic dreams of making her a star. She and Keyes quickly find common ground and grow closer, eventually developing a relationship.
While escorting her home from a tennis game, Keyes catches Jesús Bernal loitering in the parking lot, doing a lackluster job of surveilling the Orange Bowl Queen. Bernal is not paying enough attention, and Keyes beats him soundly, armed with nothing but a tennis racket.
Furious, Wiley informs the gang that Bernal has thrown away their psychological advantage by revealing himself and their plans too soon. To regain it, Wiley announces that he's devised a new plan.
Bernal, simmering with humiliation and aching for reinstatement with the anti-Castro terrorist group he was expelled from, decides to proceed with his own agenda. Abandoning Las Noches , he sends a mail bomb to Al Garcia, whom he identifies as a "traitor" to the anti-Castro movement. Farcically, the bomb is instead opened by an over-eager Ricky Bloodworth, illegally sifting Garcia's mail for clues about the terrorists. Because of Bernal's poor construction, the bomb does not kill Bloodworth, it only injures him. Garcia never learns that the bomb was addressed to him, and the bombing is attributed to Wiley's gang.
The next evening, Wiley unleashes his new plan: buzzing the deck of the pre-Orange Bowl Friendship Cruise out at sea in a helicopter, Wiley promises to give the tourists on board some "real Florida souvenirs," and drops hundreds of shopping bags from posh vendors onto the deck - which, when ripped open by the frenzied tourists, contain live snakes. Chaos envelops the deck of the cruise ship, and one foolish passenger yells "abandon ship!" causing all of them to dive off into the ocean. As the Coast Guard is rescuing them, the helicopter flies away, but unexpectedly crashes at sea before it reaches land. No bodies are recovered.
Believing that Las Noches are dead, the Miami civil leaders breathe a sigh of relief. Keyes and Garcia remain skeptical, however, and insist that their security precautions remain in place until after the Orange Bowl Parade.
In a last-ditch attempt at redemption, Jesús Bernal kidnaps Garcia at gunpoint and drives him out to Key Largo for a flashy execution. Garcia is wounded in the shoulder by Bernal's shotgun, but Keyes manages to track them down and kills Bernal with a pistol shot.
To Keyes's surprise, the Parade comes and goes without any sign of Wiley or his gang. The next day, Cab Mulcahy writes his own front-page account of the tourist murders, revealing his own knowledge of Wiley's role in the killings and apologizing to his readers for withholding it.
The evening after the Parade is the Orange Bowl game itself. In the stands, Keyes realizes, belatedly, that Kara Lynn is supposed to make a brief appearance during the game's halftime show. With all their security measures focused on the Parade, the game is a perfect opportunity for Las Noches , alive and well, to strike. In the chaos, Kara Lynn is kidnapped and carried out of the stadium on an airboat, though one of the gang, ex-football player "Viceroy" Wilson is shot to death by a Shriner friend of Theodore Bellamy, acting as Kara Lynn's unofficial escort.
With the police rushing around in confusion, Keyes goes directly to Jenna's house and examines Wiley's old press clippings. Quickly deducing where Wiley has gone, Keyes drags Jenna along with him.
Wiley has taken Kara Lynn to Osprey Island, a small nature preserve in the middle of Biscayne Bay. When Kara Lynn recovers from her drugged sleep, Wiley is taken aback, and sorrowful, that she is, contrary to his expectations, an intelligent and unspoiled young woman. Regretfully he reveals his final plan: the surface of the island has been mined with dynamite, to be exploded at dawn, to allow for the construction of a snazzy new condominium complex. Wiley plans to leave Kara Lynn there, with the island's other remaining wildlife, just to illustrate to the greedy developers of Florida the consequences of their rampant development - as he puts it, the island's native flora and fauna have zero value for such people, but they might stop and think if their dynamite blows up the only species on earth they actually care about: "a future customer."
Before Wiley can go, however, Keyes arrives and disables Wiley with a bullet to the leg. The fisherman who dropped Keyes off refused to wait around, so Keyes demands to know where Wiley anchored his boat. At first, Wiley refuses to tell, prepared to let the dynamite claim himself, Keyes, and Kara Lynn all at once. But he is horrified to learn that Keyes has brought Jenna along, and surrenders the boat's location. To Keyes's surprise, he refuses to go along with them, preferring to stay on the island.
As they speed away from the island, Keyes, Kara Lynn, and Jenna look back and see an amazing spectacle: Wiley is climbing a tree (bad leg and all), trying feverishly to scare a bald eagle nesting there into taking flight before the dynamite explodes. The novel ends just as the "all clear" signal for the detonation is sounded, with the three of them whispering the same prayer: "Please fly away."