Without a Clue (1988)

"The flip side of Sherlock Holmes"

Sherlock Holmes is as dashing as ever, but with a little secret: Dr. Watson is the brains behind the operation. When Reginald Kincaid, the actor he has hired to play Holmes becomes insufferable, Watson fires him and tries to go out on his own, but finds that he has done too good a job building Holmes up in the public's mind.