After the slow-grinding, interlocking minutiae of Letters, John Barth may have thought that his readers deserved a breather, and he's given them one: Sabbatical. Set largely on a sailboat nosing along the chops of the Chesapeake Bay, Sabbatical is a chummily facetious scribble about a former CIA officer and his sweetie and all the weird, wacky things that happen to them "twixt stern and starboard." Like other Barth novels, this one ladles on the Maryland lore: the tweeting couple is named Fenwick Scott Key Turner and Susan Seckler (nicknamed "Black-Eyed Susan," after the Maryland state flower), and their sailboat is dubbed Pokey, in honor of those two Baltimore legends Francis Scott Key and Edgar Allan Poe. A comical twosome, Fenwick and Susie trade teasing wisecracks like a nautical Sonny and Cher, announcing flashbacks and flash-forwards, unfurling digressive reminiscences, bringing chapters to a close as if cutting to a...