501 : Rio
Horatio and Delko go to Brazil in pursuit of Marisol's killer Antonio Ruiz. After reuniting with Yelina Salas in Brazil, Horatio learns his brother, Ray Caine, is in too deep undercover in a drug ring run by Ruiz and Horatio's nephew. Ray Caine, Jr. is falling prey to Ruiz's lure into working as a drug mule to smuggle drugs into the states. With the stakes set high, Horatio must catch Ruiz, before Ruiz takes the life of another member of Horatio's family.
502 : Going Under
After collecting evidence at the crime scene for a murdered ATF agent who was working undercover with a criminal motorcycle gang suspected of selling illegal firearms, Calleigh is run off the road into a canal and compromises her evidence. Since almost none of the evidence is salvageable, the CSIs dig deeper to discover new evidence that suggests the agent's cover was blown and a member of the gang took him out.
503 : Death Pool 100
Following a jewelry robbery and murder during a party for Miami's A-listers, the Horatio and the team discover the motive for murder is tied to a "death pool in which players legally bet off-shore on when famous people are going to die. However, the off-shore gaming ship taking the bets proves not to be is as legit as it appears when the CSIs uncover that the ship is circulating counterfeit currency into the economy.
504 : If Looks Could Kill
When a male model is run over by a car, the CSIs discover his good looks may have cost him his life in Miami's competitive modeling industry. After another male model falls to his death, the CSIs rule out the two cases are connected and evidence suggests his death is tied to a hefty life insurance policy taken out on him. Also, Natalia's abusive ex-husband is released from jail and begins stalking her at work.
505 : Death Eminent
When a local city councilman's bloated body is found in an empty house, angry neighborhood home owners move to the top of suspect list as the politics behind "eminent domain, the government's right to force people out of their homes for private development, appears to be the key motive for murder. Horatio gets an opportunity to rewrite history after the CSIs connect a missing girl's DNA found in a home owner's backyard to Judge Ratner, a dirty judge who eluded murder charges in episode #310 and the judge hearing the eminent domain case.
506 : Curse Of The Coffin
When a believer in Santeria religion, a mix of Catholicism and African voodoo, is found murdered in front of her shrine of animal sacrifices, bizarre incidents start happening around the CSI lab, leading them to wonder if the lab is cursed. While scientifically debunking any suspicions of a curse, the case takes another turn when the CSIs discover the victim was murdered over a tangled plot to recover stolen gold. Horatio prevents a car bomb from taking out the intended targets; the police who arrested the car bomber's brother.
507 : High Octane
When a man is decapitated while performing a stunt during a sideshow, kids in tricked out cars doing dangerous stunts, Horatio and his team discover the car's hydraulics had remote access indicating his death wasn't an accident. While investigating the sideshow murder, the CSIs uncover evidence that suggests the murder may have been a diversion for a plot to mine jet fuel from a pipeline running under the city and smuggle it out of the country in stolen cars.
508 : Darkroom
After one woman is found murdered and another kidnapped, the case becomes personal when the CSIs uncover photos of missing women in a safe, including one of the kidnapped victim; Natalia Boa Vista's sister. The CSIs safely rescue one of the women but when they discover she suffers from Stockholm Syndrome, they have to rely on the evidence to find Natalia's sister and the killer who poses as a photographer before he strikes again.
509 : Going, Going, Gone
A young woman murdered after being auctioned off on a date for a charity event, is discovered to have been working undercover to expose the charity host's drug dealing, but the host's drug investigation is only the start of his problems after the CSIs discover he is funding a deadly plot by a terrorist sleeper cell to blowup a nuclear power plant.
510 : Come As You Are
When a Marine recruiter is killed, the CSIs face a long list of suspects including anyone who opposes the war in Iraq to fellow recruiters looking to eliminate the competition. Hate mail sent to the recruiter from a soldier who thinks he killed his brother in combat leads Horatio and co. to re-investigate the case and ultimately expose a cover-up for the brother's murder.
511 : Backstabbers
When an alleged member of a terrorist cell (from episode #509), on trial for aiding in a plot to blowup Miami, goes on the run after almost being gunned down by her own people who think she's a trader, Horatio never waivers in the fact that she's innocent until proven guilty and as CSIs it's their job to find and protect her.
512 : Internal Affairs
513 : Throwing Heat
While investigating the death of a Cuban refugee blown up by a land mine seconds after stepping foot on shore, Det. Frank Tripp lands in the hot spot when he steps on another land mine, sending Horatio and the bomb squad into action to defuse it before it detonates. After breaking up a domestic dispute by punching the husband, Delko is slapped with a civil suit for a quarter million dollars that the husband's con-artist wife isn't about to lose.
514 : No Man's Land
Miami faces an imminent threat when a truck full of confiscated guns is ambushed while in route to the incinerator and a thousand guns go back into circulation. When the CSIs discover Horatio's old enemy, Clavo Cruz (episode #315), who he put away for murder, is behind the operation and has cohorts planning to use a rocket launcher from the heist to bomb the courthouse during his arraignment, the CSIs are in a race to stop the attack and prevent Clavo from escaping.