The Hollow Man by John Dickson Carr
The most famous of all locked-room mysteries - a classic in the crime genre.
'The first deadly walking of the hollow man took place when the side streets of London were quiet with snow and the three coffins of the prophecy were filled at last...'
The murderer of Dr Grimauld walked through a locked door, shot his victim and vanished. He killed his second victim in the middle of an empty street, with watchers at each end, yet nobody saw him, and he left no footprints in the snow.
And so it is up to the irrepressible, larger-than-life Dr Gideon Fell to solve this most famous and taxing of locked-room mysteries.