An elderly woman dies mysteriously and her priceless pink diamond disappears. Her granddaughter, Sylvia, wants the jewel found and hires Lucy James, Reno detective. The hunt for the diamond, called the PInk Carbuncle, takes them to Spain and Morocco with varying degrees of success and the bad guys hot on their trail. Clues from the grandmother's stories of gypsies and Arabian princesses converge with those of a former choir boy and a nun. They travel on camels in Morocco and encounter speeding cars in Barcelona. Tipsters attempt to throw Lucy and Sylvia off track, but with help from friendly Spaniards, the women travel through deserts, mountains and fanciful foreign locations in their pursuit of the pink diamond. But not all roads lead to Rome, and Lucy and Sylvia must come home where they meet their biggest challenge of all.