William Byrd died 400 years ago. Who was William Byrd? Born in London around 1540, he was one of the great composers of the Renaissance and a musical maverick as well. The “secret” in the program’s title refers to the small-scale Catholic masses that Byrd composed during the Reformation, specifically for persecuted Catholics to use, undetected, at home. This program, designed by Bill Barclay, is described as “part installation, part concert, and part immersive theater.” It features six singers and six instrumentalists who will be located in different parts of the Catacombs, recreating for audiences the once forbidden Mass. Each performance includes an hour-long spirits tasting and a twilight walk through Green-Wood Cemetery to the atmospheric Catacombs. —Laura Jacobs