At one time, Blood, Sweat & Tears was the biggest rock band in the world. Their 1970 self-titled debut album sold millions and won a Grammy for Album of the Year (beating out recordings like “Abbey Road” and “Crosby, Stills & Nash”).

In what the band thought was a goodwill gesture, they became the first act to tour behind the Iron Curtain — only to learn they were pawns in a propaganda ploy by the Nixon White House and U.S. State Department. At a time of great political tension at home, they became pariahs in the rock community and with their own fan base.

This has all recently come to light in the new documentary film “What the Hell Happened to Blood, Sweat & Tears?,” which screens Tuesday in New London’s Garde Arts Center. BS&T founding guitarist and songwriter Steve Katz will appear in person to perform a few songs and discuss the film. I’m fortunate to moderate the post-screening conversation — and, yes, I’ll ask Katz if “Lucretia Mac Evil” was inspired by a real person.

“What the Hell Happened to Blood, Sweat & Tears?” with Steve Katz, 7:30 p.m. Tuesday, Garde Arts Center, 325 State St., New London; $18; gardearts.org.