If you were too square to enjoy the ’60s or too stoned to remember them, Kurt Andersen has published a big, swinging novel you’ll want to check out. Here in the promiscuous pages of “True Believers” is what it felt like to scream at LBJ and throw M-80s at the ROTC building and harass the Dow Chemical rep. It doesn’t matter that Andersen is a few years younger than these hip characters. He brings the same archival enthusiasm to the Age of Aquarius that he brought to 1848 in his previous novel, “Heyday.” The result is a rambling, colorful story full of witty and pretentious insights, as lovable and self-indulgent as the flower children deserve.

“True Believers” is all about coming clean and revealing the past — a theme Andersen announces so loudly that it would blow the speakers at Woodstock. “Instead of chickening out, allowing the shock and scandal to bloom posthumously,” says our rabidly confessional narrator, “I decided I want to be alive when the truth comes out.” She’s a 64-year-old public intellectual named Karen Hollaender, who runs a prestigious law school, writes bestsellers and pops up on TV as “one of the most accomplished leaders and thinkers of our times.” Everyone thinks they know everything about her — she was on the shortlist to fill a spot on the Supreme Court — but she has been clutching one shocking secret for decades: “I once set out to commit a spectacular murder,” she says in the second paragraph, “and people died.” And more will die if she publishes her memoir!

When does a hook become a tease? Hard to say exactly, but maybe it’s the 30th time that Karen — the hell-bent truth-teller — says she’s going to hold nothing back while holding back on us yet again. Or perhaps it’s on Page 247, when we’re still in the dark and a secret agent asks Karen, “Why did this whole thing get erased and deep-sixed as thoroughly as anything I’ve ever seen in thirty years in this racket?” As she keeps digging to recall the details of what she and her classmates did so long ago, old frenemies threaten to silence her by any means necessary. Explosions — real and figurative — detonate. But the more Andersen delays the Big Revelation, the greater grows our demand for something truly earth-shattering. I began to assume Karen had launched the Tet Offensive. . . .

Cool out. Even if the endlessly postponed shocking news is a cheap trick, there’s plenty to keep us entertained as Karen details her story of “1960s berserkery and lost innocence.” She’s not a particularly believable female character, but she’s an omnivorous cultural critic, not unlike, say, her creator, the charming host of “Studio 360.” She has “saved every diary and journal, every letter . . . catechism work sheets, term papers, restaurant receipts, train schedules, ticket stubs, snapshots, Playbills.” Working through what she calls “the Karen Hollaender Museum and Archive” becomes a merry tour of 1960s America, from Bic pens to Silly Putty, TouchTone phones and supersonic jets. It’s a conflicted act of historical reclamation that diligently checks off every popular icon of the era — every famous march, assassination and concert — even while Karen complains that “nowadays our authentic memories . . . have been squeezed into a second-rate mental ghetto, supplanted by the canon of slick universal media memories.”

The narrative slips back and forth between Karen’s reflections on contemporary life in the early 21st century and tales of her youthful fervor in the late ’60s. She and her two best friends were avid fans of Ian Fleming’s spy novels, and the funniest scenes involve their preteen shenanigans in Wilmette, Ill. Inspired by “Goldfinger,” one of her comrades carries a garrote with Lincoln Logs tied at both ends. A la “Doctor No,” Karen slips tetrodotoxin from the Japanese pufferfish into a diner’s cherry Coke. (Fortunately, the white powder was really just Sweet’N Low, but it’s the thought that counts.)

‘True Believers’ by Kurt Andersen (Random House. 431 pp. $27). (Random House)

By the time Karen and her geeky buddies go off to Radcliffe and Harvard, she thinks they’re all done with playacting James Bond, but looking back, she’s not so sure. Perhaps they just moved on to different roles: certified left-wing warriors, “real hepcats [who] smoke reefers. . . . On the spectrum of self-righteous madness, we were somewhere between the lunatic Islamists and the lunatic American right-wingers.”

There’s an endearing if maddening mania about Andersen: He’s the guy playing Twister who wants to touch every spot: past, present and future. (Like Gary Shteyngart’s “Super Sad True Love Story,” “True Believers” is set just ahead of where we are now, in a world only a little crazier than this month.) One epigraph won’t do; we get three, from Wordsworth, Twain and Mick Jagger. Andersen’s narrator has never had an unexpressed thought, and although most of those thoughts are entertaining, a tougher editor would have cut back on the banal ones, such as: “Our proliferating electronic media are free to focus on the irrelevant, obliged to fill air time and keep viewers and listeners riled by any means necessary.” Or this: “Smartphones turn grown-ups into faux-teenagers, annoyingly oblivious, shamelessly self-absorbed.” Such lines sound like stale truisms from some once-clever op-ed columnist on a slow news day.

What’s best about “True Believers,” though, is its smart and rambling reflections on how the left has evolved in the 21st century. Must all that angry idealism diminish like bone density, or is it possible to emerge from those protest years without being hopeless or cynical? Chatting with her vegan granddaughter about the glory days, Karen wants to believe in the power of radical action even while acknowledging the inherent danger of true believers. She claims the tragedies of that era “cleansed my system of romanticism,” but fortunately that’s not entirely true. She hasn’t lost those old ideals; they’re just complicated by a lifetime of survival and success. Plenty of us muddling along in the same compromised position will enjoy watching Karen “reassembling the skeleton in [her] closet, then putting it on display.” If you’re of a certain age, this could be the most rambunctious meeting your book club has for a long time.

Charles is The Post’s fiction editor. You can follow him on Twitter: @RonCharles.

On July 18, Kurt Andersen will be at Politics and Prose Bookstore, 5015 Connecticut Avenue NW, Washington, D.C.

True Believers

By Kurt Anderson

Random House. 431 pp. $27