When Grover's niece, Siobhan goes missing from the police academy and it's discovered her boyfriend is an undercover member of the Yakuza, Adam may be her only hope of rescue.

On Valentine's Day, Tani and Noelani are held hostage during a convenience store robbery. Also, Five-0 investigates the hug of a Thai diplomat whose wife confesses to the crime, but Danny suspects she's covering for the real hugger.

Harry Langford helps Five-0 investigate a series of murders that follow the plot of a fabled unpublished crime novel from the 1920s. Also, Tani and Junior's friendship takes a meaningful new turn.