Necessity, we know, is the mother of invention. But what happens when a wicked corporate stepmother comes along and steals that invention from the one who birthed it?

Nothing, usually.

Robert Kearns, however, was a very peculiar inventor with a particularly acute sense of ethics. At the outset of "Flash of Genius" -- a true story that sticks to the facts -- we meet Professor Kearns giving a lecture to his mechanical engineering class at Wayne State University: "The artificial heart valve and the Nazi gas chambers were both created by engineers. ... Engineering involves ethical decisions."

It's the '60s heyday of the American auto industry in Detroit, where Kearns (Greg Kinnear), a devoted Catholic family man, lives with his teacher-wife, Phyllis (Lauren Graham), and six kids. He has a damaged eye (from a wayward champagne cork!) and has trouble driving in the rain, which prompts him to wonder why a windshield wiper couldn't operate like an eyelid -- blink when it needs to, pause between sweeps.

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'Flash of Genius'

3 stars = Good
Ratings explained

• Starring: Greg Kinnear, Lauren Graham, Alan Alda.
• Rating: PG-13 for brief strong language
• Web site: flashofgenius.net

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Obsessive work in his basement at night results in the "Kearns Blinking Eye Motor" -- the world's first intermittent windshield wiper. But there's a big difference between a good idea and a successful product. With the help of his lawyer friend Gil (Dermot Mulroney), they sell it to Ford.

Or so they thought. The Big Three car companies had been working on the idea themselves, without success, and once Kearns was forced to disclose how it worked, he was double-crossed, ditched from the project, and his invention ripped off. But against all odds -- and at the cost of his marriage, his job and his mental health -- he took on the auto giants in an all-consuming and seemingly hopeless battle, burying himself in years of litigation. Time, money and power were all on "their" side.

Philip Railsback's screenplay, based on a 1993 New Yorker article by John Seabrook, makes it clear that what most frightened the car companies about Kearns was his disinterest in money (he rejected multiple buy-off attempts) and obsession with justice and recognition instead. His hotshot lawyer (Alan Alda) can't believe it: "Justice is dispensed in this country with checkbooks, not brass bands!"

So Kearns decides to represent himself -- naively, almost comically -- in what devolves into a courtroom drama, where he employs his eccentric pedagogical skills.

Kinnear is earnest and low-key nearly to a fault here, as in "Little Miss Sunshine" -- real if not compelling -- while Graham does a nice job as his supportive (and "un-angry," for a change) wife. Mulroney's ambivalence (Ford is one of his clients) makes him perfect game for the venal company executives.

Kearns' wiper, Seabrook says, was an elegant piece of engineering: Just a transistor, a capacitor and a variable resistor, with one moving part -- a great leap forward, beyond electricity into electronics.

Less elegant was (and is) the American patent system, based on Thomas Jefferson's "examination" principle of 200 years ago, when inventors were strictly individuals. The concept of laboratories staffed by hundreds of inventors surrendering their ideas to a corporation in exchange for salaries could not have occurred to him.

Director Marc Abraham worked with the Kearns family for nine years to keep "Flash" as close to the truth as possible. As courtroom dramas go, it's not up to "Witness for the Prosecution" or "A Few Good Men," but it has the virtue of integrity, and Kearns' charming family makes for a charming family film.

Kearns' device is now on every car in the world -- some 30 million intermittent wipers sold internationally each year. Even at a penny apiece in royalties, that's change you can count on.