The Staked Goat (The John Cuddy Mysteries)

As military policemen, John Francis Cuddy and Al Sachs bonded while patrolling the wild streets of American-occupied Saigon. Over a decade later, Cuddy is a private detective making a living in Boston's back alleys. Awoken by a ringing phone at seven a.m., Cuddy is shocked to hear Sachs asking to meet for a drink that night. His old friend's voice reminds him of the time a Cagney movie inspired Sachs to say that, if ever captured by enemy agents, he would break his pinkie finger to signal to Cuddy that his death was not an accident. Sachs never shows for the drink, and the next morning he is found naked in a park, his body mangled and his pinkie broken.

To avenge his friend, Cuddy confronts a dark military cover-up, and travels back to the war zone he thought he left behind years ago.