It won't hit stores until after Labor Day. Yet, reviewers have already received their advance copies of The Given Day, the new novel by Dorchester's dean of letters Dennis Lehane.

That kind of lead time says something about the book's heft. It clocks in at just over 700 pages, for one thing. But it also dramatizes an increasingly distant, yet momentous slice of Boston history: the 1919 Boston police strike. It's a moment in the city's history that Lehane says should be given the same historical heft as the trauma of the busing crisis in the mid 1970s.

"I would argue that there were two apocraphyl events in the 20th century, when we were the center of a national debate," Lehane, who grew up steps from Edward Everett Square, told the Reporter last week. "Whichever way Boston went on this would determine: "Can emergency personnel ever strike and fight for their rights?" The entire world turned to Boston and watched how this would play out."

Like many native Bostonians, Lehane was only vaguely aware of the events of that tumultuous year, which began with the 1918 world championship win by the Babe Ruth-led BoSox (the Babe is one of the book's recurring characters) and ended with pitched street battles between striking lawmen and US troops. In between, the city was ravaged by other tragedies, including a molasses flood that swept through the North End, killing 21 people. The city was also ground zero for the so-called Spanish Influenza, a strain which went on to kill upwards of 60 million people worldwide.

"That's what I fell in love with," says Lehane. "It was one incredible year in Boston history."

After a year of solid research, Lehane set out to write about the strike, but - as often happens in his work - turned to find new strands of that era standing at the threshold. One of the main plotlines follows the struggle of black Bostonians through the character of Luther Laurence and his wife, Lila. As the drama of the police strike is dominated by Irish-Americans centered around "Danny Coughlin," the efforts of African-Americans to set up an office of the NAACP act as another engine for the book.

"I didn't decide, it was decided for me. It was originally about the police strike. This character just sort of walked into the book and said you need to put me in this book. So, it became the story about the two Americas," he said.

The year after the end of World War I, Lehane says, saw a new and violent wave of racial politics sweep the nation. It kicked up with the release of the racist film Birth of a Nation in 1915. And it was triggered too, by the experiences of thousands of African-American men who fought valiantly on the battlefields of France, only to return to home more rigidly segregated than before.

"All of a sudden you had this subset of young men who said, 'We're not laying down for anything.' That combined with the loss of 11 million jobs, it caused lots of class warfare. It was black versus whites on the streets and it became a very dangerous time to be black in America."

The Given Day is also about Boston's neighborhoods, but in a departure from his Kenzie detective series, Lehane admits that, "this is the book that for once - and maybe the only time - they will say I'm writing about South Boston."

Lehane says that the history of the strike and the three days of violent riots that surrounded it dictated the setting more than anything.

"The riots got down to the edge of Dorchester, but didn't get too close. The last pitched battle of the Boston police strike - and I mean pitched battles with cavalry charges - was at the Broadway Bridge," he said.

Recreating the Boston of 90 years ago was difficult. Lehane says he tried to avoid re-visiting the actual sites where the key events of the drama unfolded. For one thing, they are hardly recognizable today.

"You try and get your head back in 1918, but what good would it do to look for Scollay Square," he says. "I did it a little and it's really damaging, you shouldn't do it.

"In the end, it's better to let your imagination go."

If - as Lehane believes - a book's calibre can be measured in large part by the degree of difficulty for the author, then The Given Day is likely to be a gem.

"There were stretches when the book seemed outside my grasp," he admits. "The harder it is to write, the more worthwhile it will be to read."

"Every book is different. The books I most enjoyed writing have been, in retrospect, my worst books. It's not supposed to be about fun. If you're having too much fun, you're probably not doing your job."