The episode begins with a lifeguard on a beach getting alarmed on seeing in the water something that, looks like a shark fin. He rushes to the water and warns everybody in the water to get out. In the end it is shown that, it wasn’t a shark at all but a woman in a mermaid costume who is washed ashore. Callie meanwhile tells Jim that she wants to go back to med school full time. Just then Carlos calls Jim up. At the scene Carlos tells Jim that, it’s been a tradition in Florida to dress up like a mermaid for a particular show. Jim wants to find out who makes the mermaid costumes. Carlos on the other hand feels it was an accidental case of drowning, and hence asks Jim to not go through any trouble. Jim then pulls back the victim’s hair behind and shows Carlos marks on her neck, which indicates strangling.
Carlos later makes an assessment that the victim died 6 hours ago, between 1 and 4am. Daniel then tells Jim that the mermaid tail was custom made and cost $10,000. The victim’s name is Cassandra Hudson. Daniel also gives Jim her address. Jim and Daniel then scan her apartment for some clues. They check out the photos on her bedroom wall. In many of the photos they find a young man with her, who they assume to be her boyfriend. They also find all her appointments written on a calendar, and come to know that, her team is rehearsing at that very moment. Jim then pays the rehearsal a visit and meets Cassandra’s alleged boyfriend Jay Nelson, who is also the manager of the team. He tells Jim that he was asleep at home between 1 & 4 am, and before that he was at his friend Daryl’s house. Jay also tells Jim that, both Cassandra and her sister Brooke haven’t shown up for the rehearsals.
Jay is then shocked to know about Cassandra’s death, and immediately asks Jim if Brooke is a suspect. Jim tells him “now she is”. Callie meanwhile decides to take a break. Brooke in the meanwhile comes to the precinct to talk. Brooke tells Jim that she too was at Daryl’s house for his party. She admits to Jim that she took Cassandra’s car to the party, but doesn’t remember where it is. She also tells Jim that, Cassandra was alive when she saw her at Daryl’s party, and after the party she was arrested by the cops for DUI. Later, Jim is informed by Carlos that Cassandra was possibly drowned in a swimming pool, based on the chlorine found in her stomach. Colleen later tells Jim that Brooke has been arrested multiple times for DUI. Colleen also tells Jim “Brooke was as bad as Cassandra was good”. They also find out that, on the night of the incident Brooke called up Cassandra five times.
Jim is also intrigued by the fact that, both the sisters have made multiple calls to Daryl in wee hours of the morning. First it was Brooke who did so three months ago, and just recently it was Cassandra who had been doing so. Later Daryl tells Jim that he is trying to host the biggest and the baddest musical on water. It also turns out that the show was Cassandra’s idea, and hence Daryl would lose a lot of money, now that Cassandra is gone. Daryl also tells Jim how Brooke took Cassandra’s car and left her stranded. It was Jay who then gave her a lift, after the party. Hence Jay might have been the last person to see her alive. Callie, who is on a break, is meanwhile getting bored at home. Daniel and Carlos meanwhile inform Jim, that Cassandra’s body was dumped at the bay near Daryl’s house, and she was possibly drowned in Daryl’s pool.
Jim is pretty sure that Daryl isn’t the murderer, as he doesn’t have a motive to kill Cassandra. In fact he had the most to lose from Cassandra’s death. Jim instead feels, the killer is either Jay or Brooke. Later, Jim confronts Jay at one of Daryl’s parties and asks Jay for his car keys, as he allegedly gave Cassandra a ride after the party. Later Jim tells Jay that, a foamy fluid that only comes out of a person’s lungs after drowning was found on the back seat of Jay’s car. Jim also tells Jay that he has discovered, Jay took the blame for a hit and run a few years ago, but it was probably Cassandra who the real culprit from the look of things. Jay then admits that, Cassandra would have lost her synchronized swimming scholarship if she was convicted. Jim also tells Jay that he is sure Jay was jealous because now Cassandra was paying more attention to Daryl instead of him. Jim then figures out, Cassandra didn’t leave with Jay, but came back to Daryl on the night of the incident.
Jim consequently arrives at Daryl’s house with a forensic team to gather clues. Carlos later tells Jim that the foam on the back of Jay’s car was vomit, and it was most possibly Brooke’s. Jim also hears the voice messages Brooke left Cassandra that night. In the messages, Brooke taunts Cassandra for having a relationship with Daryl, but hiding it from everyone. Brooke’s five phone calls to Cassandra were actually 5 angry messages. Later at Daryl’s house, Jim finds Brooke practicing in the pool. She tells Jim that she would be replacing Cassandra as the new lead of the show. She tells Jim that the show was actually her idea, but when Daryl met Cassandra, he completely forgot about it. She also tells Jim “good guys like Jay never fall in love with girls like me”. She tells Jim that she isn’t all bad. She then hands her phone over to Jim, and also tells him all that she remembers from that night is doing flaming shots of Vodka. Cassandra’s car is then discovered.
In the car they find a DVD which shows Cassandra rudely telling Jay to focus the camera on her as she is the star of the show, and not on the rest of the team. Jim assumes, Jay was getting tired of Cassandra’s attitude, and pays him a visit. Jim tells Jay that he has figured out, Jay wasn’t in love with Cassandra anymore, and he was in love with Brooke instead. Jay then admits to Jim that he told Cassandra he didn’t like the way she was treating Brooke, but Cassandra didn’t agree. He and Cassandra then got into an argument, and that is why Cassandra got out of the car that night. Callie later tells Jim that, she has decided to switch fields and is ready to do anything health related. Carlos meanwhile calls Jim and tells him that, Cassandra’s body was in Daryl’s boat. Jim then arrives at Daryl’s house and tells Jay that he is there to arrest Brooke.
Jim then tells Jay that Cassandra stole $5 million from her investors, including $40000 from her parents. Brooke was afraid Cassandra would screw over her parents, and hence they had a fight. Jim then tells them that Cassandra had booked a one way ticket to Switzerland, and was going to run away even before the show opened. Brooke is shocked to hear all this. Jim then realizes who did it. Daryl is next shown, being questioned by Jim at the precinct, for Cassandra’s murder. Turns out, Daryl and Cassandra were together stealing money from investors.
Daryl then found out Cassandra had stolen the $5 million, and kept it all for herself. Daryl discovered this on the night of the incident, when he was trying to access their business account online. He then tells Daryl how he did it. Daryl admits to his crime and is taken away. Jim later encourages Callie to take up a job of a head nurse in Atlanta, although it means the two of them living in separate states. Jim assures her that, things will work out. The episode ends at this point.