"I'm really glad we're doing this," says Nash Watson McBride. "I'm really glad because it's recognizing a lot of America's past – and how we can get past it."

Nash is speaking on his last day of ninth grade. He's a baritone in the Philadelphia Boys Choir and Chorale, and he's excited about the choir's concert at the Kimmel Center at 4 p.m. Sunday, when the theme will be, in a word, American freedom – the sacrifices made for it, the triumphs over history's many obstacles, and the future that might be.

"We have a lot of great music, and the story the show develops is really interesting," says Nash. "My dad did a lot of work for the second half."

Nash's dad is the eminent musician and writer James McBride, the same James McBride whose memoir The Color of Water: A Black Man's Tribute to His White Mother was on the New York Times best-seller lists for two years in the late 1990s, and whose novel The Good Lord Bird won the National Book Award in 2010. Not a bad guy to help create a program for your choir concert.

A self-described "choir dad," James is a big fan of the choir and Nash's role in it. "He's had a great run and has had a wonderful time," James says from Paris. "A lot of people don't appreciate what the choir is, or the kind of really good work it is doing."

Boys Choir artistic director and conductor Jeffrey R. Smith approached James and suggested they work together. In a tight window of only two months they created a words-and-music story based on the Underground Railroad and its "conductor," William Still.

Still, a Philadelphia businessman and philanthropist, not only helped more than 800 people escape slavery but also wrote The Underground Railroad Records, a meticulous diary of the system's operations. The second half of Sunday's concert begins with Still talking about his work. Interwoven with that story is a selection of spirituals and other music. (One piece is by famed American composer William Grant Still, a distant relative of William Still.)

"We want to give people a taste of what was going on in Philadelphia during the slavery era," the elder McBride says. "This was a mass movement of thousands of people, moving day and night, many of whom were aiming for Philly, which they saw as the promised land. In reality, almost all the real action took place in Philly, much of it at the home of William Still."

There's a tonal difference between this and previous ways of telling this story, he says. It involves "getting past the myth, Uncle Tom's Cabin and so forth, and the Hollywood machine," and telling of a resilient country with the humanity and will to work past the blight of slavery.

"We want people to leave with a sense of pride, not shame," James McBride says. "Pride in what America has accomplished in ridding itself of this malady, as opposed to feeling as if they owe somebody a debt."

People may not be aware of how how central Philadelphia was to the Underground Railroad, or of Still and his heroism. And for McBride, the real story "isn't easy for the Hollywood machine to tell." That story includes the sharp division among Americans, even in ostensibly free-state Pennsylvania, about slavery, race relations, and equality. It also includes the strong, principled resistance by people like Still, by Quakers, and by other abolitionists in town, particularly in the Vigilance Committee of the Philadelphia Anti-Slavery Society.

But, says James McBride, "you don't want to knock the audience over the head with pain and suffering. Who wants to be made to sit and watch Twelve Years a Slave?  Slavery was more than that. There were many moments of incredible humanity, of love and togetherness, even of humor,, and the more aware of that we are, the better."

James says it has been a great ride working with Smith, whom this experienced musician calls "really first-rate as a conductor and composer," and being involved with music arranged by the late Moses Hogan, who was James' classmate at Oberlin Conservatory. "A lot of good things came together, and very quickly, to make things happen."

Nash McBride says that "this performance does take a lot of work and energy, but I have a lot of respect for Mr. Smith, our director, and I love the music we're doing."

What his dad is most excited about is Sunday's liberating, joyous story, a story that is all Philly. "Whatever sickness slavery was," he says, "it made slaves of us all, not just a few. By ridding ourselves of it, we all became free."

Philadelphia Boys Choir & Chorale. 4 p.m. Sunday, Verizon Hall, Kimmel Center, 300 S. Broad St. Tickets: $24-44. Information: 215-893-1999, kimmelcenter.org.