CHATHAM, N.Y. — In a wooden barn on a country road in this Columbia County community, a stage is marked out for rehearsals of Elizabeth Diggs' new play "Grant & Twain." At the kitchen table in the farmhouse nearby, Diggs and director Regge Life talk about the period production that, beginning Thursday, will launch the first full fall season in PS21's new year-round 99-seat black box theater just a stroll away.

"Grant & Twain" begins with much-admired general and former president Ulysses S. Grant broken and bankrupted at 62 by a humiliating financial swindle.

Mark Twain, nom-de-plume of humorist author Samuel Clemens, is 13 years younger and in his prime; not yet white-haired and white-suited, with "Huckleberry Finn" soon to be published.

Both men are Westerners who know the great Mississippi river well.

"Grant was a modest person, [without] ambition to be acknowledged as great," Diggs said. "Twain was the opposite, he loved the limelight."

Grant agrees to write his memoir to provide for his family, not knowing he will soon face death from throat cancer. Promising him riches and success, Twain persuades Grant to let him publish the memoir, and devotes the next two years of his life to what became the biggest best-seller in American history — and Twain's proudest achievement.

Award-winning playwright and New York University professor Diggs began work on the play six years ago after reading that memoir. "I was stunned by how beautifully written and what an exciting story it was," she recalled.

Finding the play's structure took Diggs some time. She created all the dialogue, using only a few historical quotes. While she has written about other historical figures such as Florence Nightingale and General Custer, she considers the Civil War "the biggest political drama in this country."

"The more I learned about Grant, the more amazing he seemed," Diggs said. Both North and South honored him for his determination and war-winning strategy. She regards his popular reputation as a drunk and a butcher "mostly wrong."

Grant and Twain were rock stars of the Gilded Age, Diggs explained. Twain idolized the general, calling himself like many others of his era a "Grant-intoxicated man."

That the two most famous men in America came together was "a remarkable story of an amazing friendship," Diggs said.

Still, it was so uncharacteristic of Twain to do what he did. Grant knew he had limited time to fulfill his mission, and aroused and unearthed in Twain a shared passion, Diggs said. It was one of their bonds.

Diggs had worked politically with PS21 founder and president Judy Grunberg in the past. At PS21's new building dedication last fall, Diggs thought it would "be amazing to do the play up here, in the theater that Judy built." Grunberg readily agreed.

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The cast, mostly from New York, includes Michael Sean McGuinness and Todd Gearhart as, respectively, Grant and Twain plus Carole Monferdini, Kevin Craig West and local residents Gregory Boover and Nicholas Haylett.

Both Diggs and Life have been upstate neighbors for over 30 years, "part of the `old gang' that left New York City early on," Life said.

Diggs figured they would be "simpatico" after he directed one of her favorite plays, "God of Carnage," last fall at Shakespeare & Company in Lenox.

"Grant & Twain" is still evolving at PS21, as Diggs trims dialogue and incorporates Life's ideas about structure. "He has such clear instincts about what is going on," Diggs said.

Life welcomes the opportunity to "put his fingerprints" on "Grant & Twain," having developed new plays during his early career in New York as well as recently at Shakespeare & Company.

"I'm not trying to stage a museum piece or static history," he explained. "I'm bringing it to the level of the personal, being in the room with these men and the people around them.

"That's how we learn about history and about ourselves as Americans, the good and bad of how this country was built."

Among the voices in the play is Grant's valet Harrison Terrell, whose descendants became one of the most prominent African-American families in the country.

For Life, Grant's strong anti-slavery stance and commitment to protect the emancipation proclamation by making it settled law was "a revelation."

"We're going to really make that known to those who see the play," he said. "I'm always looking for opportunities to tell the full history of America."

"Grant's presidency was about trying to integrate four million former slaves as full citizens," Diggs explained. "That was his legacy. He understood the wound that had to be healed in our country's history.

"It's a story that hasn't been finished."