Dennis Lehane grew up in the Dorchester neighborhood of Boston and has spent most of his career writing about that specific place with the kind of intimate, unromanticized knowledge that only comes from actually living somewhere. His debut A Drink Before the War (1994) introduced private detectives Patrick Kenzie and Angela Gennaro working the Boston neighborhoods Lehane knew from childhood. The sixth book in that series, Gone Baby Gone (1998), became a film directed by Ben Affleck that was better than most crime adaptations had any right to be.
Lehane's standalone novels are where his literary ambition is clearest. Mystic River (2001) is a full-blown American tragedy about three men whose friendship was fractured by a childhood trauma, reconvening around a murder. Clint Eastwood adapted it with Sean Penn and Tim Robbins. Shutter Island (2003) is a psychological thriller that earns its twist. And The Given Day (2008) is a genuinely great American novel, set during the 1919 Boston Police Strike, operating at a scale most crime writers never attempt. If you haven't read Lehane, he's one of the few genre writers who belongs in a conversation about American literature.
Patrick Kenzie and Angela Gennaro are private detectives working in the toughest neighborhoods of Boston. Start with Book 1, though each novel is substantially self-contained.
Lehane's standalone work is where his literary ambition shows most clearly. These can be read in any order.