Everyone has begun to notice a change in Hook Foot's behavior. Eugene offers to speak with him and discovers he met someone special on the island. He reveals the news to the group and Hook Foot explains how he met Seraphina. She gave him a seashell necklace and reveals he is going on his first date with her. Eugene and Rapunzel offer dating advice, but they are completely opposite of each other. In order to help better prepare Hook Foot for his date, Rapunzel and Eugene go and meet Seraphina. Much to their surprise, they discover that Seraphina is actually a mermaid. Afterward, Eugene and Rapunzel continue to offer advice and even accompany Hook Foot on his date with Seraphina to help in any way they can. However, Hook Foot has trouble expressing his feelings for Seraphina and Rapunzel and Eugene find themselves getting into a bit of a fight with each other in regards to how Hook Foot should be around Seraphina.
Eventually, Hook Foot finally lets go of his worries and insecurities and lets out a sweet romantic side. They both find themselves growing closer and soon Hook Foot confesses his love. Seraphina is shocked and has something important to confess too, but they are soon interrupted when they are attacked by the fish creatures called Vodniks. Everyone fights them off until they are captured. Hook Foot discovers the reason why they are after Seraphina is that she is a thief, who stole a valuable yet delicate Pearl that is contained in the necklace Seraphina gave Hook Foot. The Vodniks that are after her are underwater law enforcers. While upset and hurt that Seraphina used him, Hook Foot’s hurt feelings are quickly washed away when Seraphina confesses she truly loves him and they both decide to runaway together. However, the Vodniks continue to try and capture Seraphina. The group escapes captivity thanks to Shorty and reunite with Hook Foot. Together, they keep trying to fight off the Vodniks, but in the end, Seraphina willingly gives herself up in exchange for Hook Foot and the others safety. Hook Foot and Seraphina share a sad goodbye with Hook Foot giving Seraphina his own Hook as something for her to remember him by.
After Seraphina leaves, Hook Foot is sitting on the beach all day sorrowfully. Meanwhile, tons of crystals of mermaid tears are washed onto the beachside. Hook Foot picks up the pieces and walks along the beach in the sunset.
- Mandy Moore as Rapunzel
- Zachary Levi as Eugene
- Eden Espinosa as Cassandra
- James Monroe Iglehart as Lance Strongbow
- Jeff Ross as Hook Foot
- Paul F. Tompkins as Shorty
- Katy Mixon as Seraphina
- Dee Bradley Baker as Vodniks
- The title is a reference to the 1998 comedy film There's Something About Mary.
- Rapunzel does the narration in this episode.
- This episode noticeably begins in media res ("in the middle of things") before starting from the beginning.
- Eugene makes a reference to him being "a vault" in regards to keeping secrets from "What the Hair?!".