An anesthesiologist who worked in a beauty clinic is discovered swinging from a rope in his two-story condo, but the investigation points to murder, not suicide. The case intensifies when it's learned that the doctor lost a patient the week before during routine plastic surgery and that the victim's husband believes she was killed.

Josh Dalton, a hot, young reporter for the Miami Sun, witnesses the murder of his friend, a city councilman's aide, in Miami's drug district, the Golden Triangle. Josh, who was suspiciously unharmed in the attack, claims that they were only down there on a story, but Horatio believes that there's more to the situation. Later, another writer from the same paper is found shot to death inside the trunk of her car, which was reported stolen. Now, as the evidence rejects Josh's version of what happened, the CSIs find themselves entangled in the world of fast-paced journalism and learn that there is a dangerously fine line between the truth and what sells newspapers.

An adult film actress is found strangled in the park and the CSIs must find the killer. Blood and human tissue are found under Ashley Anders' nails and the DNA matches that of the CEO of the company that distributes her films – and he's a registered sex offender. Also, Calleigh discovers his answering machine audiotape on which he makes a threat against Ashley. However, there is an accident back at the lab with this crucial piece of evidence and Delko was the last person to handle it. Now, IAB's Rick Stetler is put on the case, much to Horatio's dismay, as the CSIs try to uncover further evidence in order to find the girl's killer.

E-mails and text messages trigger a mass gathering of students to perform a random task on a golf course. However, as the crowd disperses, the body of a high school student is found. The original message triggering the "flash mob" is traced to a high school senior whose father is a high-powered defense attorney. The case changes direction when Horatio and the team learn that the schoolmaster's daughter may have had something to do with the murder and evidence reveals that the victim was having an affair with his chemistry teacher.

A murder investigation takes Horatio and the team into the world of speed dating. Richard Laken is found killed by a tire iron outside a lounge following an evening of speed-dating. The team discovers his car is covered with acetone, which traces back to one of the female guests. She reveals that she dated Laken and he dumped her, so she doused his car with nail polish remover for revenge, but she didn't kill him. Now, when Horatio and the team learn that Laken recently witnessed a serious assault at a Miami Heat basketball game, they are on the hunt for two perps instead of one.

When gang-related gunplay goes down in an emergency room, Horatio and the team must find the gang members responsible. The evidence suggests that an orderly in the hospital recognized the wounded gang member, who possibly killed one of the orderly's friends and alerted gang members to his location. However, the evidence doesn't match up and the CSIs discover that a cheating girlfriend, not gang retaliation, may be behind the shooting. Meanwhile, Ryan questions a mother in the emergency room after her story regarding her child doesn't add up.

Someone uses a laser light to blind a pilot and bring down a jet, which carries $1.2 billion in checks to be delivered to banks on the eastern seaboard. The crime scene evidence reveals a victim, a young fundraising socialite, who was inside the plane but killed prior to the crash. Now, although the team has little to work with since the victim's wealthy family is opposing an autopsy, Horatio must follow the money trail. Meanwhile, Calleigh works on the case with her ex-boyfriend, Detective Hagen, and their romantic history could cause problems for both of them.

A former high school football star is murdered at a reunion, the CSIs must find the killer. The victim was the big man on campus in high school and there are a lot of guests at the reunion with reasons to resent him all these years. Now, the team must investigate everyone, from the head cheerleader to the school misfit, to see who held a decade-old grudge big enough to kill. Meanwhile, Horatio and Delko arrive at a crime scene and discover that it's already been processed, leading Horatio to uncover further information about his brother possibly being alive.

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 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.

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.

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.

The episode picks up straight where "One of Our Own" left off. Horatio and Delko have arrived in Rio de Janeiro to hunt down Antonio Riaz, who ordered the hit on Marisol. The problem is that Horatio can't stop thinking about his late wife, and Brazilian authorities aren't being very cooperative. While there, Horatio runs into Yelina and finds out that Raymond is missing again. Ray Jr., now fourteen, teams up with Brazilian authorities and will stop at nothing to bring his father home safe, until Horatio learns the terrible truth... Raymond is already dead. Now Horatio must stop his nephew from getting himself killed trying to chase a ghost.

When strange accidents occur in the lab, the CSI team is spooked during a death investigation involving voodoo. As Halloween is near everyone starts to think that the lab is cursed.

After a wealthy businessman is killed at a charity event the CSI's first suspect his wife who was hosting the event. The blood evidence is thought to belong to the wife or her two secret twin sisters but leads the investigators in another direction after the victim is not who they thought he was.

There's a serial killer on the loose marking all of his victims with a Y on their chests and one or more of the csi's lives are in danger in this season 5 finale

Horatio's son goes missing when a prison transport is attacked. Upon learning the identity of Kyle, he is targeted in order to get at Lt. Caine, who must find him before it is too late.

Meanwhile, Ryan causes tension with his former colleagues when he is hired as an expert witness for the defense.

Kyle's mom shows up in Miami and she is the widowed wife of a billionaire. She wants Kyle back and will do anything to get him back.

When a man is killed due to a fake 911 call, Horatio must face off with a private investigator who is systematically destroying the team. The PI also digs into the team's personal lives and gets both Calleigh and Eric pulled off the case.

Horatio delves into Delko's past to find the killer who targets the motel Delko is staying at.

When a flight attendant is murdered, the CSIs uncover all the dirty secrets of airplane travel.