One of a number of sharply humorous books with fantastical underpinnings written by this author before his untimely death from heart failure, Turnabout has been filmed once (a hideous 30's version bearing little resemblance to the book) and inspired a shortlived television series during the 1970's.
The storyline is familiar: unhappily married couple somehow switch bodies, hijinks and hilarity ensue. What makes Turnabout special is it's sexual frankness, unheard of during the Depression years, and the swift presentation of comedic material. The portion of the novel dealing with the husband's pregnancy will have readers howling with laughter. It's guaranteed to make you laugh out loud.
If you like Christopher Moore, Tom Robbins or the Neil Gaiman of Good Omens, read this book, or any of Smith's other works. Try one, you'll go on to the others, I guarantee it.