Magnum and Higgins take a major step forward in their relationship. At the same time, the past comes back to haunt them when a previous suspect becomes their client. TC aims to scale up Island Hoppers. Rick gets a new business partner.
Magnum and Higgins re-examine a fatal arson investigation at the request of TC and Mahina, leading to a sinister discovery. Kumu volunteers with Rick at a veterans’ crisis call center.
Magnum and Higgins are hired by a University of Oahu dean to quietly investigate a professor who has been accused of having an inappropriate relationship with a female grad student. TC and Katsumoto take Cade and Dennis on a father-son camping trip.
After a high-stakes homicide case falls apart at trial, Katsumoto asks Magnum to help him stop a killer from walking free. Higgins helps Jin Jeong with a mystery of his own.
Magnum and Higgins agree to help a teenage Amish boy who has traveled to Hawaii in search of his runaway sister. Rick sets out to find TC a date to the Marine Corps Ball.
Magnum and Higgins are hired to find a missing gamer whose online friends believe he might be in trouble. Jin Jeong enlists the help of TC in a treasure hunt after his ex-partner gets out of prison.
Magnum and Rick race to find a missing witness who can exonerate an innocent man accused of murder. TC tries to repair his relationship with Mahina after being released from the VA.
Magnum and Higgins enlist Katsumoto to go undercover when a chef at a high-end restaurant goes missing. Kumu works with Cade at the Cultural Center, confronting one of America's darker chapters - the internment of Japanese Americans in the wake of Pearl Harbor.
Magnum and Higgins try to help Zhao, a close friend of Kumu, recover her life savings that was all lost to a scammer. TC becomes increasingly frustrated at the lack of progress in his recovery and pushes everyone away.
Magnum and Higgins go to work for a dangerous and controversial client. Kumu and Shammy help move TC to a veterans' rehab facility. Rick flirts with a woman who works at the marina.
An armed hit team lays siege to Robin's Nest. TC is badly injured while Rick fights for his life. Mid Season Finale
Magnum and Higgins take on a case that sends Higgins inside a psychiatric hospital. Katsumoto and his son, Dennis, head to the mainland to look at colleges, but their trip takes a harrowing turn when a run-in with a local turns ugly.
Magnum and Rick make a shocking discovery in the Capt. Greene case. Higgins and TC head to Maui to help an eccentric billionaire find the owner of a pesky drone that has been harassing him. Shammy helps Kumu after an incident occurs at La Mariana.
Magnum and Higgins investigate the robbery of an elderly man suffering from Alzheimer’s. The ohana tries to help TC overcome a past trauma.
Katsumoto's hearing date has arrived and he will learn if his career in law enforcement is over for good or not. Magnum and Higgins are hired to investigate a man their client believes committed murder. Rick's suspicions grow on their relationship.
Magnum recruits Katsumoto to help find a missing tourist. Higgins and Kumu attempt to solve the murder of a beloved dog. Rick enlists the aid of TC after he accidentally loses Magnum's pet mouse, Roberto II.
Magnum and Higgins search for a CEO who has mysteriously vanished. Rick braces for a visit from his wild-child little sister, Ruthie.
Katsumoto takes a job providing security for a chart-topping K-pop star. Higgins and Rick find themselves in peril while trying to help Rick's friend. Magnum harbors suspicions about Capt. Greene's death.
Magnum and Higgins go undercover as lifeguards in order to solve a murder. Jin Jeong wins a storage unit auction and enlists the help of Rick and TC upon finding a stolen military medal.
Magnum and Higgins weigh the risks of pursuing a relationship. Rick juggles being a new father and running La Mariana. Katsumoto tries to figure out his next move.
