LONGMEADOW — Dr. Andrew Lam’s latest book, “Repentance,” is a historical novel based on the exploits of the 442nd Regimental Combat Team, a group of Nisei soldiers who fought valiantly in Europe while many had families incarcerated at home in internment camps.

“Repentance" is being released Wednesday, May 1, the beginning of Asian Pacific American Heritage Month and the 75th anniversary of the date the 442nd headed into battle in 1944.

“They would go on to etch their names in history as, per capita, the most decorated unit in U.S. military history,” Lam said.

They won 21 Medals of Honor, 52 Distinguished Service Crosses, 560 Silver Stars and an unprecedented seven Presidential Unit Citations. The 14,000 men who ultimately served in the 442nd won 9,486 Purple Hearts; one of their most famous members was Daniel Inouye, who won the Congressional Medal of Honor and was the second longest-serving U.S. senator in history.

“They fought valiantly and sacrificially because they wanted to prove, beyond a shadow of a doubt, that they were loyal Americans,” Lam said. “Those who won the Medal of Honor did truly extraordinary things like lead ‘banzai’ charges against German machine gun nests, expose themselves to fire to flush out the enemy and throw themselves on grenades to save their comrades.”

They volunteered in the face of extreme prejudice and bigotry against Japanese Americans. Although the 442nd volunteers from Hawaii had not been interned in camps, many of the volunteers from the mainland had been.

“Their own government first forced them into ‘assembly centers’ set up at county fairgrounds and racetracks, where they were often housed in horse stalls; and then they were transferred to one of 10 isolated internment camps … in some of America’s most desolate places,” Lam said.

He described “Repentance” as a “riveting, suspenseful family drama” that is closely entwined with the history of the 442nd Regimental Combat Team. “It will appeal to readers who like character-driven historical fiction, and anyone interested in World War II history.”

It is about a Japanese American war hero who has a secret so awful he’d rather die than tell anyone — one so entwined with the brave act that made him a hero that he’s determined never to speak of the war.

Decades later his son, Daniel Tokunaga, a world-famous cardiac surgeon, is perplexed when the U.S. government comes calling, wanting to know about his father’s service with the 442nd Regimental Combat Team. Something terrible happened while his father was fighting the Germans in France, and the Department of Defense won’t stop its investigation until it’s determined exactly who did what.

Like many authors, Lam said he writes about what he knows because that’s the only way to be authentic as an author, which is paramount because it’s easy for readers to see through anything that isn’t genuine. “I know a lot about history, medicine, being a husband and father, and being Asian American. All of these inform my writing and certainly, my Chinese American heritage has had a significant impact on what I choose to write about.”

He encourages learning from the past to reduce the chance of history repeating itself.

“We have to remember these lessons and teach them to our children,” Lam said. “That’s one of the reasons I wrote ‘Repentance,’ to shine a light on an inspiring group of extraordinary American heroes who volunteered to fight for their country even though all of them had endured severe racial prejudice, and many of them had been locked up in internment camps at home.”

Lam, of Longmeadow, is the author of “Saving Sight” about his work as a retinal surgeon and “Two Sons of China,” a World War II novel. His writing has appeared in The New York Times and The Washington Post.

Born in Philadelphia and raised in central Illinois, he earned a degree in history from Yale University, where he studied military history and U.S.-East Asian relations. He attended medical school at the University of Pennsylvania, followed by specialty training in ophthalmology and retina surgery at the Wills Eye Hospital in Philadelphia, where he also served as chief resident.

Lam is currently an assistant professor of ophthalmology at the University of Massachusetts Medical School and Tufts University School of Medicine, a partner at New England Retina Consultants and an attending surgeon at Baystate Medical Center in Springfield.

His love of history compels him to write books. His father was a cardiologist, revered in their community in central Illinois. “I could tell that a medical career would be very fulfilling,” Lam said. “In the end, my decision was simple — I wanted to spend my career helping people, so I chose medicine.”

But he never lost his love of history.

(“Repentance”, 308 pages; Tiny Fox Press LLC. is available on Amazon in paperback for $15.95 and Kindle for 7.95. It can be found also at bookstores, on BarnesandNoble.com and on AndrewLamMD.com.)