Rising to the rank of captain, Elliott was put in charge of a black salvage-and-repair company in the still segregated Army, arriving in Okinawa in July 1945, just after the terrible battle there. He excelled in his position, and the experience seemed to fill him with patriotic ardor. He wrote passionately to his wife about Franklin Delano Roosevelt, General MacArthur and especially Dwight Eisenhower, whom he would later admit to having voted for in 1952. He always harbored, it seemed, a desire to belong to a wider America, even as he saw its shortcomings.

Unbeknown to Elliott, though, his assignment to command black troops was the end result of a desire by military intelligence, wary of his “communistic” tendencies, to exclude him from sensitive work while in the Army. Before his file was finally sealed, some 14 F.B.I. agents would interview 39 “confidential informants” about him. Their investigation would culminate in Room 740, but it would not end there. Even after HUAC had finished with him, the F.B.I. sent agents to interview Elliott’s employers whenever he got a job, knowing it would likely cost him the position. The consequence was a series of agonizing sojourns back and forth across the country, as Elliott sought to find and keep gainful employment, badly straining his family and his nerves.

“A Good American Family” is intercut with Maraniss’s deep dives into the lives and backgrounds of all those other “spokes,” before, during and after the hearing in Room 740 — an effort to explore one congressman’s amazement that even some communists hailed from “good American families.” Here are his father’s radical friends who went to fight (and die) in Spain, along with his lawyer, fellow witnesses, the professional informer — a five-foot grandmother and high school dropout — who had ratted out Elliott, along with the prosecutor and leading inquisitors on the committee. Maraniss is able to spare some sympathy for the corrupt, drunken Democratic chairman of HUAC at the time, Representative John Stephens Wood, an inveterate racist with an appalling secret in his past — whose society wife would have little to do with him after she discovered his Cherokee ancestry.

This is, in the end, a fascinating confluence of America, and if the story drags in places — we don’t really need to know that there were 17,000 varieties of American apple by 1905 — more often one is bowled over by the vibrancy of that vanished nation. It’s a world where David’s sister listens to a new song called “Shake, Rattle and Roll,” and the family watches mesmerized as exquisite lines of Detroit cars appear every summer. Elliott’s wanderings take him to an Iowa newspaper that grew out of a strike by union typographers. Later, he sees his revered new publisher, William T. Evjue of The Capital Times, in Madison, talking and laughing in his office with Carl Sandburg and Frank Lloyd Wright. Did we ever live in such an America? Did we just dream it?

After a long travail, Elliott and Mary Maraniss and their children would come through, buoyed by their unflagging optimism and faith. (Remarkably, the book’s cover photo, of the Maranisses posing in front of the Statue of Liberty, was taken after Elliott’s ordeal in Room 740.)

For all of Maraniss’s research, a mystery remains at the heart of “A Good American Family”: Just what were his parents, and especially his father, doing in the Communist Party in the first place? This is a question Maraniss cannot answer, because his parents, for one reason or another — shame? embarrassment? an effort to spare their children? — rarely spoke of it. About the furthest his father would go was to admit that he had been “stubborn in his ignorance about the horrors of the Soviet Union.” But this gives us little insight into how this great American spirit ended up stuffing himself into a closet of dreary Russian dogma.

In the end, even in the best of families, some things remain secret.