On the fourth anniversary of his father's death, McGarrett meets a woman who helps him reopen the last unsolved case his dad worked on before he died.

It's Halloween and Five-0 must track down a serial killer who is copying murders depicted in a cult slasher film. Meanwhile, McGarrett must help Jerry after he is kidnapped by the counterfeiters he has been tracking.

With the help of an ex-HPD officer-turned private detective, Five-0 tries to solve the homicide of a woman who was working for a hula dancing company that is actually a front for an escort service.

McGarrett enlists Joe's help after Danny and Chin are arrested for deadly past transgressions.