The Watchman by Robert Crais

When a wealthy young heiress witnesses a brutal murder, Joe Pike—ex-cop, ex-Marine, and one-man army—is hired to protect her. But danger follows at every turn, and Pike soon finds himself in a deadly game where every move could be his last. Gritty, fast-paced, and fiercely intelligent, The Watchman cements Robert Crais as one of the masters of modern American crime fiction.