The fourth season of CSI: Miami premiered on CBS on September 19, 2005 and ended May 22, 2006.
The team must find the connection between the two crime scenes; the killing of a drug dealer and the rape of a well-off family member.
The team investigates the death of a foreign exchange student, the search for two missing teenagers, and the robbery of 10 million dollars in golden bars.
The search of a missing 17-year-old girl, whose trip to Miami turns into an ongoing nightmare.
Horatio and the team are trying to figure out how to free an innocent young man after a harsh interrogation with Frank Tripp sends him to jail.
Three suburban housewives on a girls' weekend in Miami are the prime suspects when the hotel's handsome pool boy is found murdered. When Horatio is tipped off that his team is facing a surprise efficiency review, he must trust Calleigh, Delko and Ryan to work together to find the killer. However, when they independently follow the evidence, each discovers that their analysis points to a different killer.
The CSIs must race against time when all evidence in a murder case points to Horatio. When a murdered woman is discovered, Horatio admits that he was seeing her and that he was the last person to see her alive. Although the evidence logically points to Horatio as the killer, our CSIs must now dig deeper to find the real killer and learn who would have the motive and the method to frame him.
(Crossover episode with CSI: New York, Season 2 Episode 7.)
A crossover episode that concludes on "CSI NY" begins with a convicted serial killer who escapes after sabotaging an airplane that was flying him from New York to Miami, where he allegedly buried a body. After fleeing the crash site, the man goes on a killing spree and abducts a college student. Mac Tayor arrives to help Horatio track the killer since Mac originally arrested the man in New York.
The CSI's are called out to investigate the murder of a young woman who was about to sign her divorce papers. Soon the husband turns out to be the ideal suspect. The only strange thing about the case is the murder weapon: a nailgun. The case becomes complicated when one of the CSI's is attacked when he returns to the crime scene and ends up in hospital.
Eric Delko is at the bank, following an ATM taking his debit card, when three robbers wearing ski masks rush in. Delko knows he can’t win against the three robbers but when one of them tries to rape a girl it ends in a shootout. The security tape leads them to Miami University and to the robbers next target and Horatio manages to arrest one of them. The trail leads to a videogame named “Urban Hellraisers” and when Ryan Wolfe starts playing it, it turns the similarities between the game and the actual crimes are very big. It’s up to the team to catch the robbers before they commit a crime much more serious than the last one.
A drug lord is gunned in his Coconut Grove mansion and a suspect arrested at the scene claims he sells marijuana to Delko. Stetler, from Internal Affairs, investigates and the case quickly gets personal when Horatio gets involved. As for the shooting, the CSIs learn that two gunmen may have been involved. Also, Calleigh makes a major decision concerning her job.
Horatio hunts for the man responsible for a brutal rape on a woman years back, after new DNA testing technology finds the convicted rapist innocent.
The CSIs investigate the brutal murder of a man who was learning how to pick up women at a hot nightclub. Meanwhile, Horatio tries to help out Marisol, Eric Delko's sister, who was arrested on drug charges.
The Mala Noche strike again and it's up to the CSIs to bring them down once and for all. Also, MAJOR secrets are revealed about the characters and their love lives.
When evidence shows that a series of murders is linked to organized crime, Horatio and the team are instead lead to a pair of film students who have screenplay that contains the details of the crimes.
When Horatio's nemesis, Walter Resden targets someone close to him, Horatio tries to stop him. Also Eric Delko's relationship with Natalia is tested when she thinks she may be pregnant.
Alexx’s DNA is found throughout her neighborhood where she is suspected to be responsible for the death of a convicted child molester. The CSI team soon learns that mindset of the neighborhood could lead to any of community wanting the man gone. The team must find out who the real killer was to clear Alexx.
What appears to have been a horrible car accident claims the life of a woman. The evidence turns up more information and another body. During this intense murder investigation Natalia must confess a secret in order for the case to be solved.
After a man is found not guilty of his wife's murder the CSI team finds evidence to the contrary.
After a group of wealthy women are robbed at a luxury day spa, evidence leads the CSIs to believe that this is a part of a much larger car chopping scam and each of these women are being targeted for a home robbery. Matters become worse when Horatio discovers that Marisol was also at the spa during robbery and he must now protect her when her life is threatened. Meanwhile, Ryan must deal with the fallout after he freezes during a shootout.
The CSI team must try to find out who is trying to kill a young couple who are released from prison. The couple was made out to be “media darlings” and soon find that not everyone though of them as darlings. Calleigh must work with her ex-boyfriend to help solve the case.
The CSI team must locate a woman who has been kidnapped and dialed a wrong number on her cell phone. To try and find the woman the team must first figure out whom the kidnapped woman was trying to call in the first place. Marisol has a difficult decision to make and Horatio helps her. Natalia is surprised when Ryan asks for Delko's permission to take her out on a date.
A cruise ship that is docked in Miami is the scene for a double murder. The team investigates the long list of potential suspects but soon find that the list is dramatically decreased when the CSI's find a large amount of money is missing from the victim's stateroom. Horatio and Marisol's relationship evolves.
The team is sent to investigate the death of a local celebrity, who is found murdered in her bathtub. The list of suspects includes her musician boyfriend, her assistant and her rival. The search for a young abducted girl is triggered, and Horatio tells Delko of Marisol and his plans.
The Mala Noche gang trial is obstructed when the defendant goes free with the help of the witness who is testifying. When a hit ordered by the Mala Noche gang on Horatio finds the people he loves lives are in danger. Delko finds that an ex-lover is disturbing any woman who he is now close to.
In this thrilling season finale, the loss of one of their own is the first hit the lab will take. Getting back to the lab to process the evidence, they find it has been taken over by Federal Agents looking for stolen money from a previous case.