It's called Taking Detective Stories Seriously: The Collected Crime Reviews of Dorothy L. Sayers! It's a collection of the crime reviews she wrote for The Sunday Times from 1933 to 1935. With, of course, a rather long commentary by Martin Edwards. Not really the kind of book you read from cover to cover, but great to dip in now and again. I'll probably write it up once I'm done. She doesn't spoil anything, and her voice is terrifically witty with some great turns of phrase (I especially enjoyed one week where she compared the set of books she was reviewing to racehorses at the track).