U.S. Sen. John Edwards, in the media glare of a presidential campaign, carries on a clandestine love affair … and he thinks no one's going to find out?

South Carolina Gov. Mark Sanford disappears to "walk the Appalachian trail" … and he figures he'll never be missed?

Financier Bernie Madoff steals billions in a mammoth Ponzi scheme … and he imagines that people won't notice?

These are spectacular liars. Most of us are pikers.

We're not in a league with Edwards, Sanford, Madoff and Dr. William Shumway.

What? You don't remember Shumway, a cancer researcher who said he'd found a cure when he hadn't?

Actually, that's understandable. Shumway isn't real. He is the central character in "Secret Order," a taut drama of deception that has opened the Studio Theatre series season at the Repertory Theatre of St. Louis.

Between these liars and the rest of us, it's mainly a difference of scale. As TV's Dr. House reminds us, everybody lies. Mostly, we understand why. We lie to protect ourselves, to gain an advantage, maybe to protect or to hurt, somebody else. We say that the meal was delicious when it wasn't; we say the check is in the mail when it's not; we say we understand when we never will.

Without lies, social interaction as we know it probably would be impossible. That's the comedy engine behind the new Ricky Gervais movie, "The Invention of Lying," and Jim Carrey's 1997 opus "Liar, Liar."

On the whole, however, we tell small lies, lies unlikely to be discovered and of little consequence if they are. We understand that; we use them just to function in the world.

But what about stupendous public lies that seem destined to fall apart, dragging the liars down with them? What makes people tell stories like that?

Playwright Bob Clyman explores that question in "Secret Order." Curing cancer would be a magnificent achievement, yet it would be impossible to lie about it because scientists would need to be able to repeat the experiments that stopped malignant cells. Cells don't lie, even if people do.

But people lie for different reasons and in different ways, which is what intrigues Clyman. A psychologist in New Jersey, Clyman gives dishonesty a lot of thought. That's because people lie to him all the time.

To make time for his plays (he's written about 10, nearly all produced), Clyman has specialized in child custody evaluations for family court.

"I look at he said-she said situations all the time," he explained. "When people think they might lose what means most to them — their children — they may say anything. I don't hold that against them. But it does bring out an interesting kind of behavior.

"Losing the chance to cure cancer can bring out interesting behavior, too."

By setting his drama in a high-powered laboratory where temptation takes the form of research grants and Nobel prizes, Clyman gives his audience a chance to be as dispassionate about lies as he strives to be. Very few of us tell lies about curing cancer. We're not likely to identify with the characters.

As the play proceeds, we're not likely to want to, either. All of the characters lie. On the other hand, does anyone set out to tell a big lie? It's hard to be sure.

In "Secret Order," Shumway has discovered a very promising new way to make cancer cells turn themselves off. (The made-up science is good enough for stage purposes.) Reports of his work reach Robert Brock, who lures him from the University of Illinois to the institute he runs in New York.

But things soon take a turn for the worse: The research is flawed. Lies of omission metastasize into lies of commission. That's not good for science, and it's not so hot for the truth.

Brock, tasting triumph, doesn't exactly know what's going on. But shouldn't he?

"That's the arrogance of power," Clyman said. "What makes some men successful is their inflated, can-do sense of themselves. Seeing what you can get away with turns into a measure of your strength. But that same quality is self-destructive. You think you can figure a way out of anything."

That's not Shumway, out of his depth politically, under time pressure and eager to please Brock. Can he really hope to turn things around if he just gets a little more time? Isn't he too smart to believe that? Or is self-deception stronger than brains?

The other characters, a student and a surgeon, raise honesty issues, too. Near the end of the play, the surgeon even raises the issue of the issue: "Just how real are any of the things we think we know?"

That's a provocative philosophical question, but not exactly a ringing cry for truth above all. Maybe it doesn't need to be. Maybe truth — just telling the truth — is harder than it looks because in life, unlike the laboratory, it's hard to know what is really what.

"There are very few outright sociopaths," Clyman said. "My sense is that, in their own minds, people are always trying to do the right thing. But they may be self-deceiving, and self-deception can become conscious, willful deception."

Clyman makes the same argument in "Secret Order," a play about true-and-false, black-and-white issues that's written in shades of gray.