Agatha Kimball, a wealthy blind woman, is being blackmailed and she hires Magnum to pay the blackmailer.
Having once been hired by wealthy, blind Agatha Kimball to find her missing grand-daughter Amy, Magnum's services are once again called upon by his elderly friend after she has been contacted by a black-mailer claiming to have some important information about Amy. She instructs Magnum to pay the man and get rid of whatever the information about Amy is without investigating further, but when Agatha is nearly killed in a series of suspicious accidents, and when the black-mailer is shot dead during the delivery of the ransom, Magnum decides he must ignore instructions and investigate just what trouble his elderly friend and her granddaughter are in. He delivers the money, only to see the blackmailer shot and killed by an unknown assailant after the delivery. Upon heading to Maui to learn the nature of the information that the blackmailer knew, Magnum discovers that the woman he knows as Amy is not actually Amy at all: she is a friend of the real Amy who wrote the letters to Agatha after the real Amy became addicted to drugs and then drowned in a tidal wave at the beach. The man who tried to save her but failed was the blackmailer, who turns out to have been hired by "Amy's" husband - the man behind the accidents. Magnum kills "Amy's" husband in a shootout, and he falls into the water. Once made aware of what has happened, Agatha willingly forgives Amy and proclaims that she is her granddaughter at heart.
- Tom Selleck as Thomas Sullivan Magnum IV
- John Hillerman as Jonathan Quayle Higgins III
- Roger E. Mosley as Theodore "T.C." Calvin
- Larry Manetti as Rick Wright