A team of firefighters responding to a call are shocked when a burning man literally slams into their truck. Sid determines the victim died from smoke inhalation when toxic fumes filled his helmet, and a patch from the Mercury 3 shuttle and the victim's odd trajectory make the CSIs wonder if he did in fact fall from the sky. Sid also makes note of a meat thermometer found by the victim and apparently used to stab him. Kendall Novack offers another theory when she reassembles wood and ceramic debris from the scene and concludes that the victim was a luge racer. Kendall shows Danny and Lindsay that the luge their victim was using was homemade, but notes that his suit was state-of-the-art. Lindsay also notes the victim was covered in a variety of accelerants, indicating he may have been doused and set on fire. Using their victim's estimated velocity at the time he hit the fire truck, Danny and Lindsay are able to determine he was riding his board on 45th street between 6th and 8th. When they go to the location, Lindsay discovers a dip in the road that may have caused their vic to fly off it and into the air. Lindsay finds a metal wheel at the scene and Danny gets a call from Kendall: the patch was purchased off of eBay by a user named "Mercury." Danny and Detective Angell track down a luge racing match and are able to find Mercury, who identifies their victim as "Demon," aka Deckman Hollister. He admits to participating in a brutal race with Demon and to stabbing him with a meat thermometer, but denies killing his rival.
Lindsay is able to recover a logo on the metal wheel: Concrete Cowgirl. Concrete Cowgirl, Sandra Cook, is a professional luge racer with big company endorsements. The suit she's wearing in the picture on her website matches the one Deckman was wearing when he died. Danny questions her and she tells him she sent Demon the suit after he broke her official speed record. She raced down the same path Deckman took, hoping to match his speed, but she toppled over before she reached his speed. She insists she didn't kill him, saying she'd never jeopardize her career. Danny and Lindsay return to the lab to recreate the conditions for Deckman's race, and Danny recalls it was raining lightly the night Deckman died. The CSIs realize the rain would have brought up oils from the street, coating Deckman's suit. When they conclude that Deckman must have lost control and tried to stop the luge racer, they look at his shoes and realize the steel beneath the sole ignited the fire--and sent Deckman to his accidental death.
A woman's dead body is literally washed out of a public toilet. Stella identifies her as Vanessa Matlin, a twenty-three-year old social worker. Mac notices defensive wounds on her arms, and finds a knife by her body. Sid determines the wounds weren't fatal; Vanessa drowned when the public toilet filled up with water. Sid recovers red wax from Vanessa's hair and blood from under one of her fingernails. Hawkes processes the bathroom and discovers a polyurethane seal in the sink, clogging up the bathroom. Stella gets a hit in CODIS on the blood under Vanessa's fingernail: it's a match to Seth Riggin, a man Mac helped put away for the murder of a single mother several years before. Mac tells Stella he's certain Seth was the killer, despite the fact that Seth maintained his innocence. After checking the evidence again, Mac pays Seth a visit while Stella searches his cell. She finds a letter in an envelope and takes it back to the lab to analyze. Hawkes traces the red wax in Vanessa's hair to a man named Vinnie Palgrave, recently fired from a port company that uses the red wax to seal bottles of port. Vinnie, a former convict paroled two weeks ago, tells the CSIs that he and Vanessa were dating; they met eight months ago on felonydate.com. He swiped a bottle of port and went to her apartment, but she broke up with him and he left angry--but he insists he left her alive. DNA evidence backs up his claim.
Mac and Flack search felonydate.com and discover that Seth had a profile on it, but deleted it. Stella has the answer: Seth was in a relationship with Vanessa. After trying to decrypt the letter in the envelope, she found his message hidden under two stamps on the envelope, urging Vanessa to "stay strong." Flack thinks Seth got Vanessa to fake an attack in order to make it seem as though he was innocent all along. They ponder how she got Seth's blood until Mac recalls a ketchup packet among Vanessa's personal effects and discovers the red liquid inside is in fact blood, not ketchup. The CSIs are still baffled by what went wrong in the bathroom, until Hawkes discovers three burned wires that controlled the self-cleaning system and the door mechanism. Mac is able to recover prints from the wire and matches them to John Szabo--the owner of a company that was outbid for the public bathroom contract. Hoping to get the city to change their mind and choose his company, he sabotaged the bathroom--with fatal results for Vanessa Matlin. Mac pays Seth one final visit in jail to tell him that his plan has been foiled.