As Magnum helps a woman find her missing cousin, Sergei, a Russian fugitive, Higgins' and Kumu's lives are put in danger when they get too close to the case.

Magnum and Higgins are shocked when one of her former MI6 teammates shows up with a fresh gunshot wound and news that "the Viper," the assassin who killed Higgins' true love, has surfaced on Oahu. Also, while Magnum's busy helping Higgins track down the Viper, he asks Rick to take over a case, a task that Rick relishes until it goes sideways.

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.

As Magnum and Higgins work a case to recover valuable stolen truffles, they also must care for a baby left abandoned at the gates of their estate, while Kumu tries to locate the infant’s mother.