Dennis Lehane, author of Mystic River, has given us an important novel about America, one I am grateful to have at a time when many truths about our racial and social history are routinely obscured by crass politicking, wishful thinking and blatant lies. “People don’t want truth,” one character in The Given Day says, referring to an industrial accident that provides a convenient excuse for a government crackdown on political radicals in post–World War I Boston. “They want certainty . . . or the illusion of it.” In 2009 that sounds all too familiar.

Lehane’s new novel focuses on a Boston family during the tumultuous year of 1919, when the city saw bombings, labor unrest and class warfare. Lest you resist the latter term as too extreme, check out the role of the Harvard football team during the Boston police strike. Lehane reminds us that 1919 was a time when an immigrant worker who dared to speak up about unsafe conditions on the job risked being labeled as a terrorist and deported.

This sobering account of the Red Summer of that year helps us better understand some unsavory aspects of U.S. culture that remain with us today. The summer of 1919 found an ambitious young attorney in the Department of Justice determined to ferret out “reds” and Bolsheviks—or, as one character says, anyone who “looks like a Slav, Italian or Jew.” His name was John (later J. Edgar) Hoover. African Americans called the summer red because of the blood that was spilled in urban race riots throughout the country—in East St. Louis, Chicago, Omaha and other cities—when whites burned down thriving black business districts and neighborhoods.

This is an exceptionally ambitious novel, which is admirable in itself. I’m glad to report that it also succeeds in being a gripping novel, with well-wrought characters we can believe in. Lehane’s apprenticeship as a mystery writer serves the reader well: for all its length, this is a page-turner. Fans of Lehane’s earlier detective stories will still be entertained, but this is a book that will preach.