The Yeomen of the Guard, Light Opera Works, at Northwestern University, Cahn Auditorium. Strangely dark and emotionally ambivalent, this 1888 operetta by William S. Gilbert and Arthur Sullivan veers far from the comic formulas of the same team’s H.M.S. Pinafore and The Mikado. Set in the time of Henry VIII, it concerns a condemned prisoner who escapes from the Tower of London by wooing two women: the daughter of a tower guard (or yeoman), whom he finally dumps, and the betrothed of a traveling jester. (The jester’s mistreatment by his unexpected rival gives ironic meaning to the subtitle “The Merryman and His Maid.”) Gilbert’s libretto weds Victorian and Elizabethan idioms; the clownish wordplay between the jester, Jack Point, and the “assistant tormentor,” Wilfred Shadbolt, could have come straight from lesser Shakespeare.