Detective Duke O’Shaughnessy is Malone’s former partner and professional foil. A second-generation Irish cop, Duke embodies the entrenched xenophobia and institutional rot of the era. He’s gruff, racist, and quick with his fists—but not without a sense of duty. Duke genuinely believes he’s one of the “good ones,” though his moral code is warped by fear, pride, and a deep-seated belief in ethnic hierarchy.

Despite their differences, Duke maintains a grumbling protectiveness over Malone, part big brother, part begrudging rival. He disdains Malone’s education and poetic airs, yet respects his instincts. Their bond is battered but intact, and Duke’s eventual breakdown and violent death in the depths of Red Hook serves as both tragedy and symbol: a man undone by the very darkness he couldn’t comprehend.