Magnum's luck takes a tumble when he injures his ankle while training for an upcoming charity sports event, and if his foot doesn't heal in time, his place will be taken for the race. But his luck looks set to fall even more when he finds that prostitute Leslie Emery, who he met when he was working as a hotel detective, has now given up working as a call girl and has recently taken a job as a waitress at the King Kamehameha Club, and wants to hire him to help her find her missing sister. Although she is well-meaning, Leslie has proven to cause nothing but problems for Magnum, and sure enough, in next to no time they are up to their necks in chaos, as they uncover that Leslie's missing sister is involved with powerful political figures.

It is almost the 4th of July, and Higgins heads to Maui for an annual writers conference, and Rick and T.C. take a trip away, leaving Magnum on the Estate to face the horror of his tax audit. But that's nothing compared to the terror yet to come when Magnum becomes the focus of a crazed, obsessed killer, who repeatedly phones him with cryptic nursery rhyme riddles of upcoming killings. At first he thinks it is a crank caller, but the full reality of the situation hits home when a prostitute is murdered in circumstances reflecting the clues given, and the menacing calls continue, with the deranged killer boasting about his crimes and giving clues of the next one.