Holmes Is Where the Heart Is Magnum, P.I. : Season 4 Episode 18

As he continues his memoirs, Higgins recalls the spring of 1976, when old friend from Sandhurst, David Worth, arrives in Honolulu to attend the funeral of a mutual friend. Insisting that his name is Stanley Sigerson, Sherlock Holmes's most frequently used alias, and that Higgins is Watson, Holmes's faithful friend, David firmly believes that their friend was murdered by none other than Moriarty, Sherlock Holmes's arch-nemesis. In the name of friendship, Higgins indulges David in his investigation, even though his suspicion that David is insane is borne out, and is shocked to discover that David's assertion that their friend was murdered was absolutely correct.