Ace Ventura (Jim Carrey) is a private investigator living in Miami, Florida, who specializes in retrieval of tame or captive animals. Despite the success of his methods, he does not receive many assignments and therefore cannot pay rent or repair his battered 1970's Chevrolet Monte Carlo. His eccentricities make him the laughingstock of the Miami-Dade Police Department.
At Joe Robbie Stadium, Snowflake (the bottlenose dolphin mascot of the Miami Dolphins) is kidnapped two weeks before the team is due to play in the Super Bowl. The Dolphins' owner Mr. Riddle believes the team will lose the Super Bowl unless Snowflake is returned. He orders his head of operations Roger Podacter (Troy Evans) and chief publicist Melissa Robinson (Courteney Cox) to find Snowflake. Ventura is hired to solve the case and discovers his first clue in the form of a rare triangular-cut orange amber stone, which he speculates to have fallen from a 1984 AFC Championship ring. Ventura then tries to find his culprit by tricking each member of the championship squad into showing their rings. Despite locating every player on his list, he is unable to locate the ring missing a stone.
Later, Podacter mysteriously falls to his death from his apartment, which Robinson and Ventura go to investigate. Although Miami Police Lt. Lois Einhorn (Sean Young) insists it was suicide, Ventura proves it was murder. While trying to find how Podacter's death is connected to Snowflake's disappearance, Ace becomes romantically involved with Melissa. He learns of a former Dolphins kicker named Ray Finkle, whom he missed during his earlier investigation because Finkle was a mid-season replacement. Finkle had missed the potentially game-winning field goal kick at the end of Super Bowl XVII, causing the Dolphins to lose the game and his own career to fail. Finkle's entire home town turned against him and his family, and the demoralized Finkle became obsessed with Dan Marino, whom he blamed for the missed kick. Upon learning that the team gave Snowflake his number and taught him how to kick a field goal, Finkle went insane.
Having discovered Finkle's obsession with Marino, Ventura is sure Finkle is the culprit but cannot find him. Ace also believes that Finkle was the one that murdered Podacter when Podacter found out who he was. Later Ace and Melissa go to a mental hospital at Tampa where Finkle was last seen eight years ago. Ace poses as a mental patient and searches Finkle's belongings, discovering a newspaper article about a missing woman coincidentally named Lois Einhorn. Ace calls Emilio (Tone Lōc), a detective friend of his, and tells him to look for clues to a relationship between Einhorn and Finkle. Emilio tells Ace that he found a love letter from the deceased Podacter in Einhorn's desk. Studying this information, Ventura learns that Lt. Lois Einhorn is actually Ray Finkle in transgender disguise.
Super Bowl Sunday arrives. Ace follows Lt. Einhorn to a remote warehouse by the docks, and the two engage in a short struggle before all of the Miami Police force arrives to arrest Ace on Lt. Einhorn's orders. They are stopped by Melissa, who has Emilio held hostage at gunpoint. Lt. Einhorn screams at the police officers that Ace is behind it all and that he kidnapped Snowflake and was trying to kill Marino and her. Ace explains Lt. Einhorn's motives and claims that Lt. Einhorn is actually Ray Finkle. Lt. Einhorn denies all of Ace's accusation, which leads to Ace trying to find proof of his accusations by first trying to remove the lieutenant's hair, thinking it to be a wig - it turns out to be her real hair. Next, he rips open Einhorn's blouse to find two perfect feminine breasts. In a last-ditch effort, Ace rips off her skirt, assuming there to find her penis, but instead appears the normal figure of a woman. Just as Ace is about to give up on his theory, Marino alerts Ace of a bulge he can see in Lt. Einhorn's silk panties. Ace now with concrete proof against Einhorn makes a short humiliating speech directed at Einhorn and spins her violently around to reveal Einhorn's/Finkle's huge penis and testicles tucked between her/his legs in her/his panties to the whole Miami police force. Ace reveals that Einhorn actually killed Podacter because "he found Captain Winky!" The whole Miami police force, Marino, and even Snowflake react in total disgust at this revelation of Lois Einhorn's true identity as Ray Finkle, suggesting Finkle had kissed all of them as he did with Ace. In a rage, Finkle makes one last attempt to kill Ace but he flips him over the wharf into the water. Finkle comes up spitting out water in ruin and total defeat Ace then finds the ring with the missing stone on his hand to finalize his theory that Lois Einhorn is no doubt the disgraced Ray Finkle, Finkle is then arrested for all of his crimes.