This collection has an intiguing premise. Five writers from the Detection Club (plus Russell Thorndike) wrote six stories of the "perfect murder", and then Superintendent George Cornish, who had recently retired from the C.I.D., was tasked with explaining how the police would have caught all these clever criminals and outwitted the best detective writers in Britain. I enjoyed his commentaries - they surprised me with how speculative they were. He doesn't stop at the facts given in the stories; he re-imagines them, and sometimes…