Magnum returns from a case to find that Higgins' old Army commander is staying on the Masters estate, under tight security, until some I.R.A. members he helped capture are tried. Two secret intelligence agents hire Magnum to protect the brigadier and foil assassins out to kill him before the terrorists' trial, but the “need to know” basis the agents insist on operating by only serves to complicate matters for Magnum.

Higgins volunteers Magnum's services to guard a wealthy socialite's quarantined dog after the attempted dognapping of the canine. Sir Algernon Farnsworth soon finds himself to be the most wanted dog in Hawaii when his former owner, aging gangster Victor DiGiorgio, needs to get him back.