It's Halloween in O'ahu, and Five-0 must track down a serial killer inspired by Frankenstein. Also, Jerry calls Five-0 for help when an armed gang raids a blood bank, and Danny must track down Grace who lied and snuck out to a Halloween party.
In order to stop a meth epidemic on the Island, McGarrett and Danny go undercover as pilots, but when McGarrett is seriously wounded, Danny is forced to break their cover in order to save his partner's life.
While Five-0 works the case of a murdered bounty hunter who apprehended a dangerous killer, Danny's ex-wife reveals a shocking secret to him that will change his life forever.
As Max prepares to say goodbye to his Five-0 ohana, they must investigate a murder during a police convention on the Island. Jimmy Buffett returns as Frank Bama.
Five-0 races to Mexico where Chin puts his life on the line after his niece Sara (Londyn Silzer) is kidnapped, on HAWAII FIVE-0. Duane "Dog" Chapman returns as himself and George Takei returns as Chin’s Uncle Choi.
