If you're a big fan of Dorothy Sayers, you might take the trouble to read "Have His Carcass." If you're not already a Sayers fan, don't bother. Her language is delightful, her characters addictive (I simply can't get enough of Lord Peter-- who can?), and her plots are, for the most part, rather ingenious. This one was exasperating by page 50, and I spent the next 200 pages wondering when Harriet and Peter would catch up to me.
So skip "Have His Carcass," but if you havn't already, by all means do read "Strong Poison." It's the book in which Lord Peter Death Bredon Whimsey meets and falls in love with Harriet Vane (the author's alter ego), and it's as good a detective novel as Doyle or Christi ever penned. The plot is clever and engaging, Sayers use of language is typically stunning, and the blossoming relationship between Peter and Harriet is the most honest, original, fresh, heartwarming, witty, charming romance since Beatrice met Benedic. And be prepared to fall in love yourself, because Peter Whimsey is, as one astute critic wrote, "what God could have done with men, if only he'd had the money." Truer words were never writ.