McGarrett and Five-0 help save an injured police dog and in turn use him to find who killed his partner and ambushed his team making a drug bust. McGarrett receives a visit by a former SEAL, who asks McGarrett for a job on the task force.
Local big shot crime boss Jimmy Okada gets hit in a rather spectacular fashion, and Five-O's old friend from MI5, Harry Langford, lends a hand on the case.
The lives of Five-0's informants are in danger when the HPD system is hacked and one ends up dead, forcing McGarrett to enlist the help of hacker Aaron Wright (Joey Lawrence), who he just imprisoned. Joey Lawrence Returns as Aaron Wright.
McGarrett and Adam join Junior at a bank heist in progress, forcing all of them to make difficult decisions in how to proceed into the bank and after the suspects. Tani has issues with a family member and gets advice from Lou.
When investigating a deserted yacht adrift at sea, McGarrett, Danny, Tani and Junior are exposed to a deadly bioweapon and the rest of Five-0 have only eight hours to find an antidote.
When Danny is shot while quarantined in the hospital with McGarrett, Tani and Junior, he's left unconscious and clinging to life, imagining a future for everyone in Five-0.
Danny, still recovering from his gun shot wound is telling his son Charlie a bed time story who Steve and a group of veterans are hunting down some fake Santas who robbed a money truck.
McGarrett rounds up every gang-related criminal on the island to find the culprit behind the killing of an FBI agent who was cracking down on organized crime.
When a corpse is stolen from the cemetery, the team races to find out who the man was and why he was taken; Adam recruits someone to become an informant; Tani receives devastating news.
Five 0 investigate the murder of the headmaster of a private school sending Tani and Junior undercover as prospective parents. Meanwhile Adam is forced to produce a huge amount of hidden money to save his life.
A flashback about the case that changed Danny's life and an answer about who shot him by meeting a woman who was married to the shooter. Jimmy Buffett returns, Alex O'Loughlin directs his first episode and plays the guitar.
A hitman, Leroy Davis (Frankie Faison), McGarrett's father failed to arrest comes to McGarrett to finally confess his crimes and admit where he buried his victims. Also, Jessie makes a dangerous decision that could ruin Adam's life.
Catherine returns to Oahu, Hawaii, U.S.A. to ask Five-O for some help in order to follow up on a lead for one of her Central Intelligence Agency cases. (#188)
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.
Duke is forced to steal crucial evidence from the police locker in exchange for his kidnapped granddaughter; Jerry goes undercover at a mental health facility to solve a murder. (#190)
Steve joins Junior and his SEAL team on a mission to capture an elusive person who is holding his mentor hostage; Gerard and Kamekona help Lou and Tani on a murder case involving art stolen by Nazis in World War 2. (#192)