At the start of the exceptional novel “Proving Ground,” Nat Dresden, a U.S. army lieutenant in Iraq, forced to follow a superior officer’s senseless orders, causes the death of a 7-year-old Iraqi boy. That tragedy looms over all that comes later.

Nat returns home to law school, but he’s confused, angry and coping with post-traumatic stress disorder. Then his father is murdered in Brooklyn’s Prospect Park, just outside his home. David Dresden was one of America’s premier civil rights lawyers. He won cases before the Supreme Court, delighted in marijuana and Bob Marley, and was hated by police for his crusades against brutality.

“Proving Ground,” by Peter Blauner (Minotaur)

The elder Dresden had been suing the FBI for $12 million for charging a letter carrier named Ibrahim Saddik with terrorism and sending him to Macedonia to be tortured — beaten, starved, waterboarded — during several years of captivity. Nat’s elegant mother, the daughter of a one-time leader of the Black Panthers, believes the FBI killed her husband to make the lawsuit go away. Nat joins with his father’s partner, Benjamin Grimaldi, to push on with the lawsuit.

The novel turns on two unknowns. One is who killed Nat’s father; the other is whether Nat and Grimaldi can win their case against the FBI. Two Brooklyn detectives are also investigating the murder. Kevin Sullivan is a red-faced, pockmarked, surly giant who is near retirement. His partner, Lourdes Robles, is still in her 20s. An unlikely flirtation arises between this odd couple.

Nat, haunted by Iraq, remains the heart of the story. Blind drunk in a bar, he blunders into a fight, breaks a fireman’s jaw and spends a night in jail. Entering a restaurant, he reminds himself that he’s smelling “burning bacon on the kitchen grill, not human flesh in a blown-up car.” He thinks himself undeserving of a woman’s love. He fails to obey the word of wisdom he learned in Iraq: siudo. The word translates as suck it up, drive on. But he believes another lesson from Iraq: Everywhere is war.

The story builds to the courtroom war between Nat and Grimaldi and the FBI. The stakes are high and the tactics are dirty. It’s clear that Saddik, the middle-aged letter carrier who was tortured in the name of national security, is innocent but no one else is, certainly not the FBI and not the good guys either. Everyone is guilty of something.

Even after the trial ends, brutal surprises keep emerging. Throughout, Peter Blauner’s characters are complex and his prose is as impressive as his plot. His gritty portrayal of urban crime recalls the work of Richard Price and Dennis Lehane — both of whom have praised “Proving Ground.”

In one nice scene, Nat visits a housing project to question the family of a murder victim. In the courtyard “Gap-toothed girls in pigtails trip across faded hopscotch squares. . . . Boys just slightly taller than fire hydrants try to heave basketballs up at crooked orange hoops without nets.” The buildings around the courtyard look like “filing cabinets for poor people.” Inside, a welcome mat urges visitors to “Come Back With A Warrant.” Nat finally meets the dead man’s son, who is named Tyrion. The boy’s aunt explains, “My brother loved Game of Thrones, so he named his child after the dwarf.”

The author Peter Blauner (Michael Parmelee)

Despite occasional light moments, “Proving Ground” is finally a statement about the horrors of war and the way they endure. In a moment of despair Nat asks what all the patriotic slogans are worth “after you’ve heard a seven-year-old gurgling for his last breath, after you’ve seen your staff sergeant’s lower body pinned and crushed to a pulp under a Humvee?” We meet this sergeant, who navigates well in his wheelchair, collects guns and angrily berates Nat for not keeping his promise to kill him when he saw the extent of his injuries.

Blauner has published six novels, including the Edgar-winning “Slow Motion Riot.” Next came a decade in television, writing for the “Law & Order” franchise and recently as co-executive producer for “Blue Bloods.” His return to crime fiction novels after a 10-year hiatus is most welcome.

Patrick Anderson regularly reviews mysteries and thrillers for The Washington Post.

Proving ground

By Peter Blauner

Minotaur. 356 pp. $25.99