Cocaine Blues by Kerry Greenwood

This is where it all started! The first classic Phryne Fisher mystery, featuring our delectable heroine, cocaine, communism and adventure. Phryne leaves the tedium of English high society for Melbourne, Australia, and never looks back. The London season is in full fling at the end of the 1920s, but the Honorable Phryne Fisher--she of the green-grey eyes, diamant garters and outfits that should not be sprung suddenly on those of nervous dispositions--is rapidly tiring of the tedium of arranging flowers, making polite conversations with retired colonels, and dancing with weak-chinned men. Instead, Phryne decides it might be rather amusing to try her hand at being a lady detective in Melbourne, Australia.