LIEUTENANT PAT ABBOTT and his lovable but slightly rattle-brained wife, Jean, have become about the most popular couple in murder fiction today. In The Indigo Necklace, Frances Crane takes them to New Orleans, where a huge wartime population has overflowed into the famous French quarter, steeped in tradition and old-world ceremony. When murder is done amidst these incongruous elements, it takes ingenious sleuthing indeed to unravel the crime! Pat...