The Black Echo by Michael Connelly

For LAPD homicide cop Harry Bosch -- hero, maverick, nighthawk -- the body in the drainpipe at Mulholland Dam is more than another anonymous statistic. This one is personal.The dead man, Billy Meadows, was a fellow Vietnam "tunnel rat" who fought side by side with him in a nightmare underground war that brought them to the depths of hell. Now, Bosch is about to relive the horror of Nam. From a dangerous maze of blind alleys to a daring criminal heist beneath the city to the tortuous link that must be uncovered, his survival instincts will once again be tested to their limit.Joining with an enigmatic and seductive female FBI agent, pitted against enemies inside his own department, Bosch must make the agonizing choice between justice and vengeance, as he tracks down a killer whose true face will shock him.