Adept's Gambit

The first Fafhrd and Gray Mouser story Leiber ever wrote finds the pair cursed by an offended power: any woman Fafhrd embraces turns into a pig, and any the Mouser embraces becomes a snail. Seeking a cure from the many-eyed sorcerer Ningauble, they get pulled into a family power struggle between a woman, her adept brother, and his master, in a tale set not in Nehwon but in a stand-in for the ancient Seleucid world.