Rick tells T.C. about finding Cade sleeping at the bar. Cade snaps at T.C. then leaves. Groom Aiden is concerned that his bride Serena is acting strangely leading up to their wedding. Katsumoto informs T.C. that Cade's mother abandoned him three years ago. T.C. wants to find Cade, to give him his paycheck. Magnum and Higgins tail Serena to a motel, where she meets a man. Magnum's borrowed laser mike reveals that Serena is being blackmailed by the man who calls her Kate. Aiden confronts Serena about her past. She says the man was her abusive ex-husband. He buys what she's selling but Thomas and Juliet keep digging. Julian catches Magnum snooping in his room. Julian is poisoned by the money from  Serena. Thomas warns Juliet. She and Serena battle. Aiden walks in and Serena changes then escapes, with Higgins in pursuit. But Serena gets away. Juliet's Mi-6 contact says that Serena is an assassin and Julian was her handler. Magnum and Higgins talk about her relationship with Ethan. They brief Aiden about Serena's past. Juliet suggests that Aiden's first wife Rebecca may have been murdered. HPD sets up a manhunt for Serena. Thomas and Juliet present their theory about Rebecca to Katsumoto. He asked them to back off. T.C. comes up with an idea where Cade might be. Higgins and Magnum determine Serena might go back for Aiden for his money, so she can escape Oahu. Juliet and Thomas catch up to Serena. She claims that Rebecca wanted Aiden killed to get out of their marriage. Serena says she fell in love with Aiden, which is why she killed Rebecca. T.C. finds Cade. T.C. tells him his story and convinces him to come back. Serena escapes and Aiden goes with her. Higgins breaks up with Ethan.