THINK OF AUTHOR SIDNEY SHELDON, and certain images arise: sex, glitz, Hollywood, babies needing clean diapers, starlets.

Yo, back up a sec. Diapers?

Well, it might happen if Sheldon and his partner, James Butler, score with U.S. Patent 4,705,513 -- "Disposable Diaper With Wetness Indicator."

It started when Sheldon noticed his granddaughter's nursemaid checking to see if the baby's diaper was wet. He wondered if there was a way for the diaper to tell you it needed changing. So, "Sidney calls me," says Butler, "and says, 'Listen, if you can develop this thing we'll go halves on it.' " (Not exactly a remake of the Thomas Edison story, is it?)

Butler describes his end of the deal as a "basic research project. That's my background." He explains the product this way. "Take a regular paper towel, then take a magic marker, write on the back of it very lightly so it doesn't show through. Turn it over. Now you can't see what you have written. Take a little water and sprinkle it on there and instantly you see what you wrote. That's conceptually it."

Unfortunately, Procter & Gamble and Kimberly Clark already held patents on similar ideas, and the project looked sunk. But not to Butler. "It's just a matter of how you approach it," says Butler. "You have to find your niche." He sees the diaper as a novelty item, "the type of thing you'd maybe buy for a baby shower or as a cute little present." A manufacturer will insert the liners with the patented wetness indicators into a production run of otherwise normal disposable diapers.

So, will "Sidney Sheldon's Diaper Line" duplicate the megabucks success of Sidney Sheldon's Bloodline? Disposable diapers are a $2.5 billion a year industry, says Butler. "A flea-sized bite is worth millions."