This is a sequel to Fool, Christopher Moore's previous book with protagonist Pocket, the fool in Shakespeare's King Lear. A ribald tale that was, and this book continues in that vein.
Here, Moore mashes up two Shakespearian plays: Othello (a tragedy, or so I'm told) and The Merchant of Venice (allegedly a comedy). But it also brings in a Poe reference ("The Cask of Amontillado"). In fact, that's how the book gets its start: Pocket has been dispatched by his wife, Cordelia, to Venice in order to thwart yet another Crusade on the Holy Land. Unfortunately, Cordelia is also dispatched soon afterwards.
Pocket is grief-stricken. His habits of brutal (but R-rated funny) honesty, as well as his mission, anger some Venetians. And he is lured to a deep dank dungeon on the pretext of Amontillado-sampling. Not having read the Poe story, he is somewhat surprised to find himself being bricked up in a damp cell.
Surely he's doomed? Well, no. See the book title. Somehow he has a fearsome (but inexplicably sexual) monster on his side.
Moore turns some well-known Shakespearian characters around. Shylock is not particularly pleasant, but he's honestly angered by the injustice shown to Jews in medieval times. And Antonio isn't a nice guy, he's one of the plotters against Pocket.
Surprise non-fictional character shows up on page 214. Did not see him coming.