NCIS: New Orleans Season 1 Episode 15
Le Carnivale de la Mort
Petty Officer Toussaint Patrice is stabbed to death during a Mardi Gras parade. The team learns that he was earlier thrown out of the VIP area of a wild club after a fight over a spilled drink. His wife says that he was acting erratically, his car was missing, and he shouldn't have been at that club in the first place because he was three years sober.
The club's owner, who was the man Toussaint was fighting with, says that Toussaint was already stabbed when they got into their tiff, and that Toussaint had a gas mask with him. The police find Toussaint's car, which contained a number of cannisters containing isoflurane, a medical anesthetic, which had been stolen from a medical supply warehouse.
Toussaint and his wife were having money troubles, and she reveals that he was volunteering at a sober-living facility.
The team identifies the killer as Cyd Lawson, who was at the facility with Toussaint. Going to Lawson's place, they discover a meth lab and Cyd himself dies of an overdose, but not before revealing that there will be a big heist the next day.
Lawson's associates include Marv Williams, the probably mastermind of the heist. Pride asks his father incarcerated father Cassius, who was on Marv's cellblock, what Marv could be after. After some coercion, Cassius suggests jewels.
The team deduces that Marv and his crew are planning to use the isoflurane to attack a gala fundraiser and steal the partygoers jewels. They arrive in time to arrest all three.