The past year brought us no shortage of strange moments of political theater: We saw embattled Toronto Mayor Rob Ford knock down a fellow lawmaker in city hall. We watched Sen. Ted Cruz read “Green Eggs and Ham” on the Senate floor as part of his symbolic filibuster against the health-care law. But even amid today’s colorful political climate — which seems to constantly remind us that we should expect the unexpected — the 1946 “slap heard round the world” stands as particularly peculiar.

The incident is the takeoff point for Eric Jaffe’s “A Curious Madness,” a richly layered exploration of the thin line between wellness and madness and the extent to which our understanding of those states is sometimes a matter of perception. The slap happened at the end of World War II at a military tribunal in Japan that was similar to the Nuremberg Trials. Twenty-eight Japanese men, including generals, admirals and cabinet members, filed into a courtroom to face a panel of international judges. Just one of the defendants, a philosopher named Okawa Shumei, was a civilian.

That wasn’t the only reason he stuck out from the rest of the group: He arrived looking disheveled in a pajama top and kicked off his wooden clogs to sit barefoot during the proceedings. And then he leaned forward in his seat and slapped the head of Tojo Hideki, who had been prime minister when Japan unleashed its assault on Pearl Harbor. Some in the room said they heard Okawa shout, “This is act one of the comedy!”

The incident prompted a judge to order that Okawa undergo a psychiatric examination. When physicians determined that he was not fit to stand trial, he was sent to a mental hospital and thus was able to avoid the fate that may have awaited him otherwise: Seven of the other defendants were hanged, and the rest went to prison.

Many questioned the true nature of the bizarre scene in court that day. Had Okawa, a militarist ideologue who had propagated Japan’s cultural superiority, truly snapped? Or was this clever man shrewdly feigning insanity to get out of the trial?

‘A Curious Madness: An American Combat Psychiatrist, a Japanese War Crimes Suspect, and an Unsolved Mystery from World War II’ by Eric Jaffe (Simon and Schuster)

Jaffe’s interest in these questions is personal: The American psychiatrist who evaluated Okawa was his grandfather, a private man who told his family little about his military service (or anything else in his past). With each new discovery in his research, Jaffe wondered if his late relative’s spirit was guiding his efforts. “I thought I could give the family that revered him what his silence had denied them: the spirit, if not the contents, of the memories he’d withheld,” Jaffe writes.

The book bounces back and forth between the biographies of Okawa and the elder Jaffe. The former was born in a port town to a family of doctors, the latter to Jewish immigrants in Brooklyn. Okawa worked at a think tank by day while moonlighting as the head of a movement that asserted Japan’s divine right to lead the East and championed its power to vanquish the West. Daniel Jaffe completed medical school with a focus on psychiatry. The disorders he studied had familiar contours: His mother had been in and out of mental institutions during her adult life, with one stint in the hospital coming after she killed her infant child by throwing him out a third-story window during a psychotic episode. Melancholy and delusions plagued her throughout her life.

Daniel Jaffe eventually took his medical skills to the U.S. Army. A division psychiatrist stationed near Tokyo at a time when the military employed a relatively small number of such physicians in its ranks, Jaffe was tasked with evaulating Okawa’s condition. The slap, he believed, was the result of a mental breakdown that had been decades in the making.

Eric Jaffe’s writing is tidy if not always exciting, and his exhaustive reporting is what holds the book together. His dogged efforts to track down and talk to the few living members of his grandfather’s battalion yielded descriptions of their combat experiences in Germany that inject the account with a crucial element of emotion. And the painstaking process he describes of doing research at a National Archives facility was well worth the effort, because the documents he found there provide important context.

One of the great challenges in telling this story was unraveling the secretive personality of Daniel Jaffe. Given the few slivers of information Eric unearthed about his grandfather’s emotional makeup, he does a remarkable job of sketching a character who feels fully developed and relatable. But sometimes his efforts to tease out his grandfather’s inner feelings come off as a bit heavy-handed. For example, surely the reader can easily draw the connection between Daniel Jaffe’s mother’s mental illness and her son’s passionate study of the subject as an adult.

Perhaps the book’s best insights are the ones that aren’t specific to Okawa and Daniel Jaffe, but that tell us something broader about humanity and its response to conflict and stress: “When people looked at the slap, they saw not just what they wanted to see, they saw what they needed to see to endure in its aftermath. . . . We all saw whatever helped us carry the tragic weight of the world we’d wrought.”

In this way, “A Curious Madness” is much more than a narrow portrait of its protagonists. It is also a wider study of their cultures and the collective spirits of their countries before and during World War II.

Sarah Halzack is a writer for The Washington Post’s Capital Business section.

A CURIOUS MADNESS

An American Combat Psychiatrist, a Japanese War Crimes Suspect, and an Unsolved Mystery From World War II

By Eric Jaffe

Scribner. 304 pp. $30