Ryan is trying to earn a little extra cash by moonlighting as security at a swanky high-end fundraiser held at the local aquarium. He notices that the tank houses a very poisonous breed of jellyfish. He's asked to keep an eye on a suspicious man wandering around the party, and the suspicious man turns out to be Jesse. Ryan wonders how a cop could afford the price tag of a single ticket for the charity event, but Jesse keeps mum about the entire thing. He does seem very interested in one of the women at the party, however. Jesse denies knowing her, and Ryan and Jesse's surprise meeting is interrupted by the sound of breaking glass. A man has fallen into the tank and was immediately killed by the jellyfish.
The team arrives at the crime scene, with Calleigh teasing Jesse about his mystery woman. Horatio and Walter take a look at the balcony which gave way when the victim (a janitor) fell into the tank. They notice that there are signs of a struggle, and interrogate the CEO of the company, Max DeSalvo. Later at the lab, Calleigh has some forms filled out by the widow of the janitor. Her husband had a life insurance policy, and his wife wasn't even aware of it. Even stranger, the life insurance policy was set to pay out not to his family, but to the company he worked for. The team is given full access to the company's books.
Meanwhile Ryan and Jesse ask that the aquarium tank be drained, and sequins are discovered at the bottom of the tank. The detectives try to track down every woman who attended the party that night, asking them to bring in the dress they wore to the station so that they could match up the sequins. Jesse encounters his mystery lady again (Anna) and Natalia watches. Jesse notices Natalia there and gives her an ultimatum: if he took her out for drinks and told her everything about Anna, would she ask the rest of the team to back off on their curiosity about Anna? Natalia agrees, but Jesse never shows up at the bar and instead trails his mystery woman again.
The team discovers that there is an unusually high number of employee deaths, and all of them had life insurance policies. Digging deeper, the team discovers that one of the employees, a woman who had supposedly hung herself, was actually strangled. Horatio tracks down an accountant who confesses to helping kill her. After DeSalvo is linked to the rope used to strangle the woman, DeSalvo then confesses to killing the janitor. The janitor noticed that DeSalvo was giving his secretary expensive gifts, all the while without giving his employees decent health care. Jesse points out that the evidence is circumstantial at best, but Horatio is confident that things will work themselves out. Later, Max is shot by the brother of the woman who had been strangled.