Newcomers in that tradition who set books in the 1920s and 30s include Carola Dunn, Rhys Bowen, Catriona McManus and Dolores Gordon Smith. There are many others, but these are the ones I've read and enjoyed enough to keep reading. I seek out their new work.
Anyone thinking they'll need a dictionary to comprehend the slang of the era is welcome to sample this one online. Although it appears more American than British at first glance, there are plenty of overlaps.
Part of the fun of reading historical mystery is immersing yourself in the spirit of a different era. I was delighted to receive a link to a blog post hosting lovely film footage of London, shot in London in 1927. An example of an English-developed colour film process, it has been smoothed out to get rid of the characteristic grit and graininess of early film. I wish they'd used 1920's music when they re-released, but they didn't. It's still fun to watch, and as a bonus, I can imagine my father and his sisters whenever there's a child in the frame, as they were children in London when this footage was shot.
Let me not forget to mention, amongst 1920s series that I adore, Australia's Phryne Fisher mysteries by Kerry Greenwood. Fun, flighty and more than faintly sexy, Phryne adaptations are now appearing on PBS and ABC stations near you.
Because I truly am a glutton for the 1920s and surrounding decades, I have an ever-expanding list of titles to sample when time and opportunity permit, including Kate Morton's The House at Riverton, Robert Bastable's A Mansion and its Murder, and Laurie R. King's Touchstone. Care to suggest others I might enjoy?