Magnum and Higgins help an up-and-coming mixed martial arts fighter who is being pressured by a gang to throw an illegal fight. Also, Kumu is arrested for stealing an artifact from a collector that should be returned to its original resting place.

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 an Army ranger goes missing after returning from deployment, Magnum learns of the traumatic news he received upon arriving home and must find him before survivor’s guilt consumes him. Also, Higgins and Ethan solve the case of a missing engagement ring while on a mini-break, and Katsumoto tries spending quality time with his teenage son.

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

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.

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 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 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.