McGarrett is convinced that a psychiatrist murdered one of her patients, but will she get the last laugh? Meanwhile, Catherine discovers that an assassin is on the island and is looking for Doris McGarrett.
McGarrett and a young girl are held hostage by a diamond thief during a campout, and Kono's boyfriend, Adam, welcomes his brother back from prison and gives him an offer to become a legitimate businessman.
A college professor is murdered, but who is the killer: his boss, his teaching assistant, or one of his students? Meanwhile, Kono is assigned to protect an annoying witness released from federal prison.
Five-0 discovers the body of a missing 17 year old girl who was kidnapped 10 years earlier, and soon learn that the captors may already have a new victim. Meanwhile, Kono suspects that her boyfriend may bee keeping secrets from her.