A Christmas Eve ransomware attack on the Honolulu Police Department forces Lia to reveal a family secret to Magnum and Katsumoto.

Kumu and Higgins are in danger when Robin's Nest is under siege by mercenaries storming the estate in order to find out the true identity of the White Knight, Robin's muse and literary hero. Also, Rick and T.C. helps one of Rick's employees when his car is stolen, and Higgins finally gives Magnum an answer about if she'll become his partner.

As Magnum, Higgins and TC try to pull one over on a customs agent to get Higgins a green card, armed gunmen suddenly storm the federal building and start taking hostages.

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.

When Katsumoto suspects that one of his fellow cops is dirty and has stolen evidence, he begrudgingly asks Magnum and Higgins for help. Also, Rick and TC help Los Angeles Rams defensive tackle Aaron Donald when his tablet, that contains the Rams’ playbook is stolen.

While Magnum and Higgins reunite and work the case of a construction worker’s tragic death, TC and Shammy get skyjacked by a pair of drug runners posing as tourists.

Magnum, Higgins and Rick go undercover at a ritzy country club when a young caddie is fired after being accused of stealing a member’s golf clubs. Also, Jin’s niece, unaware of her uncle’s shady past, asks him to speak at her school.

Higgins’ therapist hires her to look into why one of her teenage patients died of suicide.

When Magnum and Higgins are hired by an anxious groom to look into his bride-to-be on the eve of their wedding, what they think is a simple case of cold feet turns into a web of lies and a life-or-death situation for Higgins. Also, TC makes a touching decision on how to help Cade.

A journalist hires Magnum to track down his anonymous source after they mysteriously go dark, and Higgins receives a new assignment from MI-6. Also, Rick’s old friend comes to the island, but TC is suspicious of his motives.

When Rick is asked to assist with a federal investigation of his childhood friend Robbie, Magnum launches his own investigation to see what the Feds really have on him Also, Kumu goes undercover in a retirement community when Higgins is hired to investigate the disappearance of a resident’s life savings.

Magnum starts following Higgins to discover what she’s been hiding, as she’s secretly assigned to infiltrate a group threatening to take down MI-6. Rick struggles after an explosion takes the life of someone important to him.

When Hawaii Supreme Court nominee Judge Rachel Park is being blackmailed, she hires Magnum and Higgins who go to extraordinary lengths to help her out. Also, with the pressure of fatherhood looming, Rick suggests changes to make La Mariana more profitable, but TC and Kumo aren’t swayed.

A bail bondsman hires Magnum and Higgins to track down a woman who skipped out on her $250,000 bond. When they locate the body of another P.I. who was previously searching for her, they partner with Det. Lia Kaleo on the case. Also, T.C. and Katsumoto team up on an emotional search for Cade’s mother.

When Magnum balks at notorious crime boss Osi Shima’s (Eijiro Ozaki) request to find his missing son, Magnum learns he’s been poisoned and has only eight hours to locate Shima’s son to earn the antidote, or else he dies.

The mother of a suspected bomber hires Magnum and Higgins to locate her teen son and turn him in to the authorities. Also, Kumu and Rick help T.C. navigate his guilty conscience when he runs into a past flame.

While Magnum helps out his friend Russell Harlan and temporarily works as the head of a hotel’s security, he investigates the death of a guest who was thrown from her room’s balcony while working on a secret investigation of her own. Also, Icepick is released from jail and is trying to keep a secret from Rick.

As a major hurricane hits the Island, Magnum and his friends find shelter inside La Mariana, along with two armed killers also escaping the dangerous storm. Also, Rick must confess to TC that he let the insurance lapse on the bar.

When Higgins is abducted, Magnum discovers its retaliation related to one of his first cases on the Island, and he, Rick and TC must break out an ex-client from prison in order to save her.

When a Marine Corps vet’s SUV is stolen with her service dog inside, Magnum and Higgins must find the car, the dog and the car thief who they believe may be an escaped kidnapping victim. Also, when TC is sued by a disgruntled customer, he asks Rick and Jin to help prove that he’s being scammed.

An incorrigible pickpocket, Jin, asks Magnum for help when a cell phone he recently lifted receives a very suspicious text message. Also, Magnum is frustrated when Higgins still won’t give him an answer to whether or not she will become his partner, and when Rick decides to make a bold career move, T.C. comes to the rescue.

Magnum must help his defense attorney girlfriend, Abby Miller, when she realizes that the client she successfully defended in a murder trial is actually guilty. Also, TC confronts Kamekona about stealing his helicopter business.

When an overenthusiastic neighborhood watch group asks Magnum and Higgins to investigate a shady character living on their block, they are shocked to find that they may have inadvertently stumbled upon a serial killer on the loose. Also, Jin’s new money laundering business leads him to want to help a new friend.

As Magnum tries to keep his new relationship a secret and handles cases solo while Higgins is away, he is tasked with finding a single mom being hunted by two very dangerous gangs. Also, while Higgins is abroad with Ethan, a misstep forces her to assist an old employer, and Rick gets some bad, but also very, very good news.

A nun hires Magnum and Higgins to investigate a mysterious and large cash donation made to a parishioner undergoing medical treatment at the church. Also, Jin’s new dog walking business takes a dramatic turn, and Rick nervously prepares to reconnect with Suzy.