Steve McGarrett returns home to Oahu, in order to find his father's killer. The governor offers him the chance to run his own task force (Five-0). Steve's team is joined by Chin Ho Kelly, Danny "Danno" Williams, and Kono Kalakaua.
(Fire Will Never Say that It Has Had Enough) The team investigates a world class hacker who turns out to be the brother of serial hacker Ian Wright, who hacks into the Hawaii State prison and releases serial murderer/arsonist Jason DuClair. He soon begins a massive wildfire. With Kono and Chin on the mainland running their own respective task forces, McGarrett and Danny recruit lifeguard and former Police candidate Tani Rey to join the task force to help out but is reluctant to join. Meanwhile, McGarrett and Danny begin to invest in a restaurant.
(Dog Days) 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.
(Your Knife, My Back. My Gun, Your Head) The team enlists an old friend when a crime boss is murdered, triggering revenge killings across the island; McGarrett and Danny work out details concerning their new restaurant venture.
(No Matter How Much One Covers a Steaming Imu, The Smoke Will Rise) 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.
(At Kama'oma'o, The Land of Activities) 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.
(Unfolded by the Water are the Faces of the Flowers) 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.
(The Royal Eyes Rest Above) 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 Trail Leads to a Diving Place, Do Not Follow After) 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.
(Death at Sea) 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.
(The Future is in the Past) 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.
(A Tall Tree Stands Above the Others) It's Christmas Eve and Danny tells Charlie a bedtime story about a recent Five-0 case involving bad Santas and a holiday miracle.
(The Round Up) 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.
(What is Gone is Gone) 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.
(The Children of Kalaihaohia) 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.
(A Coral Reef Strengthens Out into Land) 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.
(Only the Stars of Heaven Know Where Pae Is) 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.