John Dickson Carr was an American author who had spent a lot of time in the UK. Many of his books were set here, including The Hollow Man
This book includes a classic locked room mystery, a killer who apparently leaves no footprints in the snow and a clever piece of role reversal where Superintendent Hadley is the intellectual equal of the hero, Dr. Fell, rather than the not very bright sidekick
The story is undoubtedly clever, but as a circus performer in the book explains so beautifully,
" When you explain how the trick is done it always disappoints the punters"
The ending WAS slightly disappointing but Carr is such a good writer that the story carries the reader along