I'd like to see, a mad scientist, actually impress the protagonist, who then becomes interested in his work and by simply proving that 'people would support you if they actually understand what you're trying to accomplish' (you don't have to take over the world in order to legalize cheep fusion power... Just start providing cheep fusion power safely and eventually everyone will love you.
I always thought that Doc Octavius was a hero, if somewhat misguided.) With the right audience or sympathetic/supportive peers, how many 'mad' scientists would be revered by history rather than despised? Edison and Tesla come to mind. One a hands on 'lets try everything once' experimenter, the other a theoretical/mathematical visionary. Where would we be today if they'd had a Robert Boyle/Hooke relationship instead of an antagonistic business rivalry?
Would evil mad scientist still be evil with a sane MBA keeping the books and running the PR? Surely our gumshoe protagonist who has the inteligence, pragmatic ability, and (acting ability?) to have wormed in far enough to attract notice and get a monologue, could also understand the high points of the invention and plan, and sell a genius-in-need-of-a-reality-check the lab manager and sales agent that he so desperately needs.