In London's glittering underworld, a diamond robbery unfolds with cool precision until a masked stranger steps from the shadows, gun in hand, determined not to steal but to study. His calm, audacious intrusion sets the tone for a novel of crime, wit, and psychological suspense, where hidden identities and expert deception are as valuable as the jewels themselves. Elsewhere, Derby Day brings Gilbert Standerton into a world of noise, weather, and fate, where a thunderstorm tests his nerve and a roadside rescue reveals unexpected loyalty, buried connections, and the financial uncertainty behind his polished reputation. As Gilbert's engagement to Edith Cathcart grows more strained and formal, doubts deepen about love, inheritance, and the gap between public appearance and private truth. The story widens to include police bafflement over a jewel theft, Mrs. Cathcart's desperate efforts to conceal a stolen necklace and hidden debt, and a marriage marked by companionship without intimacy. In that uneasy domestic world, a wife's suspicions of her husband's nighttime absences become a painful search for meaning, as jealousy, trust, and the fear of exclusion sharpen into emotional conflict. This edition has been fully restored with modern typesetting, custom cover design.