McGarrett and Five-0 discover a Russian spy ring hiding in plain site on Oahu when a Russian nuclear attack submarine appears on the coast of Waikiki. Also, Tani is conflicted by her unnerving discovery at Adam's house.

McGarrett joins Junior and his SEAL Team on a high risk covert mission to capture an elusive target who is holding his mentor, Joe White, hostage. Also, Gerard Hirsch and Kamekona help Grover and Tani on a murder case involving masterpieces stolen by the Nazis during WWII and Tani makes a shocking discovery.

McGarrett and Five-0 take on the mob when a former boss is killed and Junior's friend Cammy Lin is on the run after witnessing the hit.

Five-0 must help Duke after he is forced to steal crucial evidence from the police locker in exchange for his kidnapped granddaughter. Also, Jerry goes undercover at a mental health facility in order to solve a murder.

Harry Langford enlists McGarrett and Danny's help to track down Lady Sophie, a teenage British royal who has run away while under his protection. Also, Grover, Tani and Junior work a 25-year-old murder case after a mysterious Betamax tape arrives at 5-0 headquarters.

Catherine Rollins recruits McGarrett and Jerry to help her track down a uranium deposit thought to be hidden on an abandoned Hawaiian island before a suspected terrorist can make dirty bombs with it. Also, when Junior falls and is trapped in a ravine, he reflects on his estranged relationship with his father.

A hitman, Leroy Davis, 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.

The ex-wife of the man who shot Danny comes to Oahu and reveals how Danny's protection during a dangerous domestic dispute when he was in New Jersey helped save her life. Also, Tani and Junior are assigned to walk the beat as uniformed officers for the day, and Adam is framed for the murder of the crime boss he has been tracking.

Adam's mission to take down organized crime on the Island goes sideways when deadly chlorine gas he was using to bait a big fish falls into the wrong hands. Also, Adam begins to doubt Jessie's allegiance.

Tani and Junior go undercover as prospective parents in order to infiltrate a private school where the headmaster was murdered. Also, Adam's life is on the line when he is held captive and forced to produce a hidden massive amount of money.

McGarrett and Danny investigate the murder of a private detective whose client was killed the same way, and Adam sends Jessie into a dangerous situation with disastrous consequences. Also, Danny's uncle, Vito, comes to town to help Danny and McGarrett get their restaurant up and running.

When the corpse of a diamond smuggler is stolen from a graveyard, Five-0 tracks down his partner, Voss, who will stop at nothing to retrieve their latest batch of contraband. Also, Adam recruits a new confidential informant, Jessie Nomura; Tani gets a devastating call; and McGarrett tasks Pua to find his and Danny's stolen tools.

When a man accused of killing his wife threatens to commit suicide, Grover reveals how he too was once on the brink of taking his own life.

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. Also, McGarrett tasks Adam with forming a new division within Five-0 to take on organized crime.

It's Christmas Eve and Danny tells Charlie a bedtime story about a recent Five-0 case involving criminals dressed as Santas and a holiday miracle.

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.

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.

McGarrett poses as a pilot to investigate the cause of a plane crash that led to the death of a pilot in an air race.

Junior and Adam back up McGarrett when a bank heist in progress forces Steve to make a potentially heartbreaking mistake. Also, Adam is forced to face an empty home without Kono.

The murder of two tourists leads Five-0 to a man suffering from multiple personality disorder, where one of them becomes violent and another is a child. McGarrett is accompanied on the case by a stress management consultant, whom Danny and the others have hired to help him manage his health.

At Halloween, Five-0 must investigate a string of murders that mirror stories from well-known Hawaiian folklore. Also, Grover is called to visit a man hours away from execution who may hold the key to a case that has plagued Grover for years.

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, who he just imprisoned.

Five-0 enlists the help of an old friend when the boss of a major crime family is murdered, triggering revenge killings across the island. Also, MacGarrett and Danny begin sorting out particulars in their new restaurant venture.

McGarrett and Five-0 work with an injured police dog who is the only witness to an ambushed drug bust. Also, McGarrett is visited by Junior Reigns, a former SEAL, who is looking to join the task force.

McGarrett and Danny recruit Tani Rey to join the task force when diabolical hacker Aaron Wright releases a dangerous arsonist from prison.