American crook Renzo Capetto sees a chance to make a bundle when a Caribbean island has a revolution. He plans to help loyalists (and the national treasury) escape on his boat, then kill the men and blame their deaths on a mythical sea monster. Trouble ensues when the _real_ monster shows up!
After the Cuban Revolution, the mobster Renzo Capetto and his lover Mary-Belle Monahan transport a group of exiled Cubans led by General Tostada to the United States with a Cuban treasure to finance a counterrevolution against Castro. However, Renzo and his gang formed by Pete Peterson Jr., Happy Jack Monahan and Sparks Moran, who is indeed the American Agent XK150, plan to steal the treasure from the Cuban people. They fabricate a sea monster to change the course to San Juan and kill Cuban soldiers. However they discover that the creature does exist and is attacking them all.
Inept government agent XK150 is on the trail of mobster Renzo Capetto, a Bogart wanna-be who is transporting General Tostada, a group of exiled Cuban nationals, and a large portion of the Cuban treasury out of Cuba. Renzo is also accompanied by Mary-Belle Monahan (an infamous gangster moll), Happy Jack Monahan (her dim-bulb gangster-in-training brother) and Pete Peterson Jr. (a hoodlum/animal impersonator). Agent XK150 assumes the identity of "Sparks Moran" and somehow convinces Renzo to add him to the gang. Renzo concocts a plan to "invent" a sea monster, so that the Cubans will allow him to change their course. The phony sea monster will allow him to eliminate a few of the Cubans, and get himself closer to the treasure. Unfortunately, someone else invented the monster first.
A crook decides to bump off members of his inept crew and blame their deaths on a legendary sea creature. What he doesn't know is that the creature is real.
- CIA agent XK-150 (Robert Towne) is working undercover in a Cuba-like small Caribbean island nation that is undergoing a revolution when he discovers that notorious international playboy, promoter and mobster Renzo Capeto (Anthony Carbone) is planning something with a group of military types loyal to the deposed regime. XK-150 learns that the loyalists leader Colonel Tostada (Edmundo Rivera Alvarez) has liberated the contents of the national treasury and plans to flee the country with the money so that he and his fellow loyalists can plan a counter revolution. Capeto is providing the boat with which the Colonel, his men and the money can leave the island. So, XK-150 posing as Sparks Moran, a notorious gum machine burglar from Chicago, infiltrates Capeto's gang as he manages to get a job on board the boat. The other gang members include Capeto's lover Mary-Belle Monahan (Betsy Jones-Moreland) - a notorious moll who used to push hard drugs to schoolchildren. Her brother Happy Jack Monahan (Robert Bean)- a tennis bum and hired killer who has developed a muscle spasm in his cheek from watching too many Humphrey Bogart movies and finally Pete Peterson Jr. (Beach Dickerson) - Capeto's top henchman who was discovered at Jones Beach where he worked as a pickpocket and has an incredible ability to mimic animal noises.
The gold is loaded onto the boat along with the Colonel and his soldiers and they set off headed for the United States. However, Renzo Capeto and his gang have other ideas. Sparks discovers that they plan to make up a story about the fantastical Creature of the Haunted Sea in order to persuade the Colonel to allow them to divert the boat towards San Juan. The Capeto gang will then bump off the Colonel and his men so that they can steal the money for themselves. Agent XK-150 constructs a radio out of hot dog sausages and pickled gherkins in order to relay a message about their plans to the CIA, but sadly has to eat it in order to avoid detection. The Colonel is suitably frightened by their stories of a legendary sea monster and agrees to the ship changing course. The gang's plan seems to be working as they begin to eliminate the Colonel's men and blame their deaths on the creature.
However, unbeknownst to anyone aboard the boat the Creature of the Haunted Sea is actually real and following them. When the boat moors off a small, remote tropical island called Isla de Barracho (Island of the Drunk) deaths start occurring that have not been carried out by any of Capeto's gang. Once he realises that the creature is real Capeto is forced into a sudden change of plan. He evacuates his crew to the island and sinks the boat in 30ft of water so that he and has gang can wait the creature has moved on then use scuba gear to go and retrieve the gold. Whilst on the island Pete Peterson meets and falls in love with a beautiful young woman Mango (Sonya Noemi Gonzalez) who can only communicate in sound effects. Sparks also discovers a phone booth on the deserted island that he can use to phone his reports back to HQ. The gang begin trying to retrieve the treasure from the boat but the creature picks them off one by one. Pete is introduced to Mango's mother Rosina Perez (Esther Sandoval) and asks for her daughter's hand in marriage. However, he and Mango are attacked and killed by the creature. Sparks meets and falls in love with the lovely Carmelita Rodriguez (Blanquita Romero) on the now uninhabited island. The film closes with the monster (Robert Bean) getting the gold as Sparks gets Carmelita.