McGarrett and Danny recruit Tani Rey to join the task force when a hacker releases a dangerous arsonist from prison.
McGarrett and the team work with an injured police dog that is the only witness to an ambushed drug bust; a former SEAL looks to join the task force.
The team enlists an old friend when a crime boss is murdered, triggering revenge killings across the island; MacGarrett and Danny work out details concerning their new restaurant venture.
When the HPD system is hacked and one of the Five-0's informants ends up dead, McGarrett enlists the help of hacker Aaron Wright, whom he just imprisoned.
At Halloween, the team investigates a string of murders that mirrors stories from well-known Hawaiian folklore; Grover visits a man who is hours away from execution and may hold the key to a case that has plagued Grover for years.
The murder of two tourists leads the team to a man who has multiple personality disorder; Danny and the others hire a stress management consultant to help McGarrett.
A bank heist in progress forces Steve to make a potentially heartbreaking mistake; Adam faces an empty home without Kono.
McGarrett poses as a pilot to investigate a plane crash that led to the death of a pilot in an air race.
McGarrett, Danny, Tani, and Junior are exposed to a deadly biological weapon; the rest of the team has eight hours to find an antidote.
Danny is shot while quarantined in the hospital; unconscious, he clings to life and imagines a future for everyone.
Danny tells Charlie a bedtime story about a case involving bad Santas and a holiday miracle.
When an FBI agent who was cracking down on organized crime is killed, McGarrett rounds up every gang-related criminal on the island to find the culprit responsible for the murder.
Grover must prevent a man who is accused of killing his wife from committing suicide.
The corpse of a diamond smuggler is stolen from a graveyard; Five-0 tracks down his partner, who is determined to retrieve their latest batch of contraband; Adam recruits a new, confidential informant; Tani gets a devastating call.
McGarrett and Danny investigate the murder of a private detective whose client was killed the same way; Adam sends Jessie into a dangerous situation with disastrous consequences; Danny's uncle comes to town to help with the restaurant.
Tani and Junior go under cover as prospective parents to infiltrate a private school where the headmaster was murdered; Adam's life is on the line when he is held captive and forced to produce a massive amount of money.
Adam's mission to take down organized crime goes sideways when the bait he uses falls into the wrong hands; Adam begins to doubt Jessie's allegiance.
The ex-wife of the man who shot Danny reveals how Danny helped save her life; Tani and Junior are assigned to walk the beat as uniformed officers for the day; Adam is framed for the murder of the crime boss he has been tracking.
A hit man McGarrett's father failed to arrest comes to McGarrett to finally confess his crimes and admit where he buried his victims; Jessie makes a dangerous decision that could ruin Adam's life.
Catherine Rollins recruits McGarrett and Jerry to help track down uranium thought to be hidden on an abandoned Hawaiian island before a terrorist makes dirty bombs with it; Junior gets trapped in a ravine.
Harry Langford enlists McGarrett and Danny's help to track down a teenage British royal who has run away while under his protection; Grover, Tani and Junior work a 25-year-old murder case after a mysterious videotape arrives at headquarters.
Duke is forced to steal crucial evidence from the police locker in exchange for his kidnapped granddaughter; Jerry goes under cover at a mental health facility to solve a murder.
McGarrett and Five-0 take on the mob when a former boss is killed; Junior's friend is on the run after witnessing the murder.
McGarrett joins Junior and his SEAL team on a mission to capture an elusive person who is holding his mentor hostage; Gerard Hirsch and Kamekona help Grover and Tani on a murder case involving art stolen by Nazis during World War II.