Jack Costello is a private detective in Miami and he finds out he is being followed by a man. He confronts him and finds out his name is Dumas. Dumas speaks with a French accent and he says he is a cartoonist and he needs Costello's image for his cartoon, but with a different name: Extralarge. Wendy is a black petty thief and when she steals an old pocket watch from Senator Pillinger and two men begin to shoot on her she seeks refuge with Costello.

A scientist arrives in Miami on a ship coming from Cuba. Detectives Extralarge and Willy have been hired to protect him. The scientist, however, is killed under their eyes without them being able to do anything about it...

Elizabeth is in a car with her boyfriend when suddenly she feels a pain in the stomach so strong she seizes a knife and stabs herself to death. Her boyfriend is charged with her murder and Dumas is present at his trial and he is struck by the boy's story. In the meantime Extralarge gets the task to find Kathy, the missing step-daughter of Laureen. Her father is dying of an unheard of disease and he desires to see her. The two girls were friends and a shade of Black Magic overhangs on them and their families.

Famous football player Long John is killed and the police believe that John was a heroin addict and that his murder is a punishment for something he did. His mother nevertheless swears that his son hated all kinds of dope and asks Costello to find out the truth whatever the result may be. Costello accepts the appointment and during his investigations notes that Cannon Ball, the best friend of long John, is scared. Also Gonzales and doctor Shuby seem to be involved. When his car blows up Costello gets angry.

Agent Blake finds the corpse of a child. It is one of a long chain. The murderer is called The Miami Killer by the newspapers. Extralarge assists the police in their investigation. All the murdered children suffered from some kind of ailment and the murderer knew his or her victims very well. The successive victim appears to be Elsie who is asthmatic and Extralarge suspects father Marthy and Elsie's teacher. Then Elsie is kidnapped. Can she be saved?

Burt meets Jack Costello after many years. Burt is a boxer and he is fleeing after a fixed match that he should have lost but instead he won. Then he vanishes. Costello finds in his office Burt's son, 'Jo-Jo' Ritchie, who had came because his father had ordered him to go to him. Then Jo-Jo cames back to Groggy where he lives and when the two of them are dining, two men arrive and kill Groggy. Jo-Jo runs away and Extralarge sets on finding him and his father.

Costello's former opponent, Gonzales escapes from prison and seeks revenge against Costello. He implicates Costello in a criminal case, who even goes to prison, but it soon becomes clear that Gonzales' plan is worthless.

Extralarge and Dumas by chance foil the kidnapping of a small girl. What apparently seems to be a normal kidnapping for the purpose of extortion hides a vendetta between drug traffickers. In fact, the girl’s father, Eduardo, is the right-hand man of the Medellin cartel. Eduardo has decided to change his ways, but the other men in the cartel will not permit him to. So Eduardo, in order to blackmail his bosses and as insurance for his life and that of his daughter, hides an enormous consignment of diamonds at a bank which he will return to the traffickers once he is safe. But luck is not with the him. A band of robbers break into the bank where the diamonds are being kept and Eduardo’s guarantee of survival disappears. Terrorized, he goes to Extralarge asking him for protection without however informing him of the real situation, while his daughter is kidnapped by the cartel’s men.....

A Chinese scientist comes to the US but is kidnapped straight away from the airport and switched for his look-alike, which soon suffers death in mysterious car accident. Young girl who says she's scientists niece comes to Jack 'Extralarge' Costello and asks him to find her uncle. Extralarge starts investigation, but someone doesn't want him to learn the truth and whole case is complicated even more when he finds out that the girl is not the person who she claims she is.

A series of mysterious murders throw the south of Florida into confusion: an individual dressed as a Ninja warrior runs through his victims with a long sword, launching incomprehensible messages. Extralarge and Dumas are appointed by the police to investigate despite the fact they have another case to solve: the protection of an important politician who has received death threats. Extralarge discovers that all the Ninja's victims were part of a team of sappers in Vietnam responsible for the destruction of a small village, Nang Ky. The death squad was headed up in fact by the politician who the detective is protecting. Extralarge also finds out that Nang Ky was the most isolated outpost in Vietnam and had become a paradise for perdition and vice run by a number of American officers who, towards the end of the war, arranged for it to be destroyed by napalm so as to cancel any trace of their abuse.

The mafia has decided to expand its gambling business to Florida as well, where however the state laws prohibit such activities. The lawyer Clemente is appointed to find ways of evading the legal loopholes and make the plan possible. Clemente discovers that the Indian reserves of America are exempt from the normal regulations of the States and prepares an action plan: he presents a project for the construction of an enormous shopping centre which, once approved, will instead become the biggest casino in America. An Indian chief, Thomas, opposes the project and is thus killed.