Harpsichordist Harry Bicket, an eminence in early music, joins the philosophically-searching foursome of the Diderot String Quartet—named for Denis Diderot, the 18th-century French philosopher who said, “From fanaticism to barbarism is only one step.” (Fans of Early Music can be fanatical too, but they don’t take that next step.) Rarely-heard gems of Baroque music are on the agenda—from composers Castello, Krieger, Durante, Muffat, and Bach—amid the cozy arches of the Crypt. A wine and food tasting begins at seven P.M., an hour before the concert. —L.J.