Such Is Death — Leo Bruce

Someone very, very clever planned this murder: the place, a remote shelter on the promenade at Selby-on-Sea; the occasion, a blustery evening in late November; the victim, somebody ready-made for a crack-of-doom from a coal hammer. Diary notes indicate someone had been planning the "ideal" murder, one which no police, no detective could solve. The murderer's gratification would be wholly cerebral, a triumph of mind over matter. However, the murderer had not counted on the clever, tenacious, unpredictable mind of that unique schoolmaster, Carolus Deene.