As CSI enters its 12th season, the team is still recovering from the fallout from the Nate Haskell case several months after its completion. Ray Langston has been let go and a new CSI supervisor, D.B. Russell, played by Ted Danson, has been hired. The Las Vegas crime lab also welcomes another new addition, a young CSI from Los Angeles and Ecklie's estranged daughter, Morgan Brady. The team must build new relationships as they solve cases that include a multiple homicide on a Vegas tram and a "Strangers on a Train" type case where numerous suspects who seem to be unrelated confess to murdering a family.
Multiple shootings and stabbings on a public tram leaves the CSI team with one witness and a lot of questions.
The team investigates the grisly crime scene of a murdered family - a grandmother, father, mother, and 8 year old daughter all killed. Morgan Brody, Ecklie's daughter who has moved from Los Angeles, has also officially joined the team. The investigation immediately leads them to their first suspect, John Lee, a peeping Tom pedophile neighbor in love with the little girl. Terrified, John confesses to the crime, but just as the team discovers that the evidence may not quite add up against him, a second person, Leslie Gitig, confesses to the crime, saying that she and the husband were having an affair. However, further investigation of the clues leads the team to discover that the murdered family was not as normal as they seemed - the family was selling drugs from the home. To complicate matters, a third suspect, Maurice Gallows, also confesses to the crime saying that he was trying to protect his drug addict son from the family. Although these individuals seem to be unrelated, Russell comes up with a "Strangers on A Train" theory: although seemingly unrelated, these three people got together to try and plan a perfect murder including throwing off the police by all three giving false confessions.
Nick is on a date at a garbage art exhibition for a local artist when he realizes one of the pieces of art, a cement block with a facial impression, has pieces of a decomposing body in it. Our team discovers the artist fished the cement block out of a ravine. Our team finds the other cement blocks in the ravine with a young girls dismembered body parts encased in cement. The victim had a flower earning which is the same M.O as a husband and wife killing team that Sara helped put away years ago. Our CSIs discover the wife, Gina, who claimed to be a victim of her husband herself, was let out of prison just 2 months ago and lives in Las Vegas. Sara and D.B pay her a visit and Gina seems to be up to her old ways, scoping out young girls at the pool where she lives. Sara is enraged by this and calls her out in front of all of her neighbors warning them about her which makes D.B realize Sara is too close to the case and grounds her. The team reaches out to warn the couple’s only surviving victim, Colleen, who suffered severe sexual abuse for years before she escaped and sent them to prison. Shortly after they speak with her, Colleen goes missing and the team works furiously to find her. Evidence at the ravine and from the cement blocks eventually leads the team to a believe Gina, who they think was the real mastermind, has taken up with a new guy and started her killings again in a warehouse by the marina. They rush there to rescue Colleen and discover a young victim in the warehouse with her abuser but it is not Gina and our team is stunned when they see who it is.
Oscar Goodman is shot in the Las Vegas Mob Museum. Our team delves into the mob history of the town. The wife of a deceased mobster who was not included in the Mob Museum, our CSIs find, has the best motive for trying to kill Oscar Goodman.
Crime scene is set in the isolated wilderness. One of the CSIs, Morgan, takes a Medivac helicopter with the victim to go over specific locations of where the crime scene is. The victim suddenly hijacks the Medivac helicopter and our team now sees this person is the suspect not the victim. The suspect kidnaps Morgan and the team works to piece together who this suspect is in order to figure out where and why he has taken Morgan before it is too late.
What looks like the ritual mutilation of a Jane Doe leads the CSI team to the freakish attractions of a 19th Century-inspired traveling sideshow. The sideshow’s MC/owner, Major Willie, and its most popular performer, a young man named Joseph Merrick, aka "The Elephant Man", are suspects after our team finds out the victim was looking to leave the sideshow. Willie would lose his best earner and Joseph was having a love affair with her. Toxicology reports show that the victim was not killed by the multiple syringes inserted in her body but by a powerful anesthetic Propofol. The cast of sideshow characters makes it tough to know who the likely suspect is but as the investigation develops, the CSIs discover the most dangerous "freak” lurks among us in the real world and the sideshow group was ultimately the victim's real family.
At the scene of a horrific car crash, the team finds three dead drivers and strangely, a human brain that belongs to none of the crash victims. Seeking to identify this "Brain Doe", the investigation leads them to the mysterious death and organ theft of a deceased serviceman whose brain was stolen from his body at a local mortuary by one of the car crash victims the night of the accident. Our CSIs discover the brain robber/crash victim, Clegg, swapped the brain found at the scene with the pathologist of an S.F.F fighter friend of his that appears to have just committed suicide. Our team follows the trail of evidence which leads to the fighter, Dempsey, and Clegg's former trainer, Pernin. Pernin was having an affair with Dempsey's wife and when he found out the fighter wanted his brain donated to science because he sought to prove he was suffering from a degenerative brain disease, CTE, Pernin hired a pathologist to remove the fighters brain and swap it with the brain Clegg stole from the mortuary. All of this was to hide the fact Pernin was supplying his fighters with an illegal performance enhancing drug to keep them fighting longer even after head trauma. The ultimate twist is when Brass finds Dempsey's wife didn't kill him but another family member did. We meet D.B's oldest son Charlie after he is suspended from a college basketball game and D.B. is concerned his son is starting to go in the wrong direction.
Three seemingly unrelated murders are linked by our CSI team and they discover a retired LVPD detective, dying of cancer, decides to complete a dark "Bucket List” of vengeance against the criminals who got away with their crimes on cases he worked on during his career. Given the detective is dying, our team knows there is an accomplice carrying out the revenge killings by making each pay for their sins in the same twisted ways that they hurt their victims. When the CSIs start to piece together this cop’s crusade, they’re shocked to discover how the roots of the killing spree extend to other members of the LVPD.
Military assault weapons on the streets of Vegas. The team investigates the murder of a man they think is an innocent rancher but find out he’s a ballistics expert. The FBI is called in and works the case with our CSIs. Two agents, McQuaid, a senior agent who has a spark with Catherine. The second is a younger agent, Pratt, Russell takes under his wing. We are introduced to a Blackwater type CEO, John Gabriel, who is actually married to an old friend of Catherine’s. Catherine sees the seemingly ideal life that her friend has and feels that may be what she is missing in her own life. The team soon uncovers that Gabriel is dirty and suspect him of the murder. The perfect life Catherine assumed her friend had doesn’t really exist and Catherine realizes her friend is afraid of her husband and may have information that she is too afraid to reveal against him. We end the episode with Catherine having a fling with Agent McQuaid and giving her friend the number to a lawyer Sam used to use when he had to get out of bad situations. Our team works to find out more about Harris and his dirty dealings.
When a naked, dead man is discovered in Doc Robbins’ master bedroom by his wife, Judy, the crime scene evidence leads to one conclusion: she may have killed the man during a romantic tryst! Despite Mrs. Robbins’ protests of innocence, the CSI’s find it difficult to remain objective as the evidence against her mounts. The twisted tale leads to suspects related to the dead man’s occupation as a genealogist, and his skill in finding familial links. Unfortunately for him, he uncovered one family secret too many.
We open on a professional hit at the law firm Catherine recommended to her friend, Laura, at the end of episode #1209. Catherine, concerned this hit is connected to her friend, goes to look for her and finds that she has disappeared. Gabriel is back and is again the prime suspect in the law firm hit and his wife’s disappearance. We learn Gabriel's Blackwater Co. also cleans up crime scenes in locations like Iraq and Afghanistan while accompanied by Marines after IED blasts. This is significant because the crime scene at the law firm was cleaned up in the same way which makes the FBI and our CSIs suspect of Gabriel's involvement. Catherine believes Laura is dead until they discover she has been hiding out. Agent McQuaid and the young FBI agent returns and you see how their relationships with Catherine/Russell grow. At the end of the episode, Catherine places Laura in protective custody with Agent McQuaid but they are ambushed by a hit squad and Agent McQuaid and Laura are killed. Catherine is filled with angry and wants to go after Gabriel full force. Vartann arrives to calm her down and take her home. Vartann drops off and moments later she feels bullets flying past her head. Catherine struggles to get to her gun and the front door so she can make it out before the hit squad kills her.
We find that Russell and Catherine are on the run and working to track down Gabriel before he tries to kill them again. The twist is when Russell, Catherine and the team figure out that Catherine’s old friend Laura was the mastermind behind all of this and was working with one of Gabriel's men, who the team is shocked to discover is Agent McQuiad, to falsely implicate Gabriel in these murders and put him away. At the end, Catherine is approached by the FBI to join their team and Catherine has to make the decision as to whether she takes the offer.
When a woman is found dead and her hair is done up '70s style complete with vintage clothes, the CSI team discovers clues that point to a killer with a hair fetish.
We meet the new CSI, played by Elisabeth Shue in this episode. She is a former work colleague of DB Russell's from the Seattle days. She is a blood spatter specialist, and very outspoken CSI. Russel goes to her for advise on a case he is now covering. She is reluctant to help out due to something that happened in the past -- something we will find out in the next few episodes. She clearly is a pistol, and knows blood spatter better than anyone else. She works with Greg in this episode to figure out the bones of this case. A man killed his ex girlfriend and they have the wrong guy for it. In the end we find that the murderer does not remember that he went into a rage and killed his ex girlfriend because he had been shot in the head, and had memory loss and black outs.
When a house is stolen right off its foundation, the CSI's find themselves caught up in a family feud, siblings fighting over the house. But when the house is found dumped in the middle of the desert, the CSIs discover a bloody crime scene in the kitchen and a mummy hidden in the wall. As the investigation twists and turns, more family secrets are revealed that forever alter the future of the family and the house. This will be the first case for our new female CSI, a showcase for her skills in blood analysis and her feisty demeanor.
The team investigates a child abduction during a blackout in Vegas. Given that back-up generators at the lab have only enough power to keep the stiffs on ice, the rest of the lab is dark and CSIs have to revert to old-school techniques to crack the case and save a missing child.
When a picture of a recently-murdered college student is uploaded anonymously to Twitter, the CSIs are brought in to track down the killer using a combination of forensic techniques and social media. The victim, Pete Moyer, was an aspiring TMZ-style journalist who had made a lot of enemies on his campus for spilling secrets and gossip on his blog. The team eventually learns that Pete accidentally fell to his death during a struggle with a suicidal classmate. Pete was recording their conversation in hopes of using it as proof that an esteemed university professor had raped her, along with multiple other girls.
The CSI team is brought in to investigate when an Alice In Wonderland themed wedding turns into a robbery-homicide. The robbers were practiced and efficient, taking jewelry and anything else of value from the wedding guests, killing the groom, and leaving very little evidence for the team to work with. When the robbers strike again at another wedding chapel, Russell digs through all the evidence carefully and figures out the robbers' MO: they commit the wedding thefts in groups of three, over a three day span. Seared flesh and melted blue latex from another crime scene prove to be the crucial pieces of evidence, as they indicate that the robbers have managed to avoid capture by posing as EMTs and using an ambulance as their getaway car. Just as the team figures out exactly who to go after, Hodges and his mother Olivia unknowingly visit a jewelry store run by the robbers and are taken hostage. Morgan enlists her father's help and gets the police to switch radio frequencies so that the robbers can't track them in the ambulance, allowing the cops to surprise the robbers and save Hodges and his mother. During the ongoing investigation into the robberies, Hodges' mother Olivia visits him at work, much to his chagrin. Morgan begrudgingly agrees to pretend to be his girlfriend and go to lunch with his mother, in exchange for him moving her to the 'front of the trace line' for the rest of the year.
When a man is shot point blank in a casino, the CSI team is called in to investigate, and they find the culprit is a young man in a yellow polo shirt. They use sophisticated face recognition software to track him through the hotel casino via the security cameras. However, there turns out to be more than one of him. In fact, there are four. They were all born of the same egg that divided four times – and four separate embryos were inseminated into four different women over time. The man who was shot was the biological father of all the boys
When Stokes learns that a man he helped put in prison is going to have his conviction overturned, the CSI team needs to prove the killer is guilty again or he will be released.
When a bomb kills an off-road race truck driver mid-race, the CSI team is called on the scene to investigate why.
The CSI team investigates three dead bodies just blocks away from a campaign dinner, they think they know who the killer is before making a shocking discovery.