Jonathan Lethem opened with a joke Thursday night at the Brattle Theatre, expressing his relief that the Red Sox had finished off the Tampa Bay Rays so that he wasn’t competing with them for viewership. Eliciting warm chuckles from the mostly full auditorium, Lethem immediately came off entirely devoid of pretense. Wearing business casual and sipping on a water bottle, the MacArthur Fellow and author of nine novels, often dystopian and genre-bending, stood at the podium to read and discuss his new work, “Dissident Gardens.” The novel, an examination of leftist radicalism through three generations of the Queens-based Angrush family, traces characters’ journeys through the Red Scare and the counterculture movement of the ’60s all the way up to the Occupy Movement. Lethem appeared rejuvenated by his departure from his usual genre, and his sincerity and enthusiasm shone through as he talked about “Dissident Gardens.”

The opening baseball joke turned out to be an apt segue into the excerpt from the novel that Lethem read, in which Lenny Angrush, a frenetic young Communist, attempts to create a professional team named the Sunnyside Proletariats. The quasi-historical scene has Lenny presenting the potential theme song for the squad, a Greenwich Village Irish folk ditty, to a bigwig and his secretary. The scene is rooted in the actual push for a New York team after the departure of the Giants and Dodgers for the West Coast in the late 1950s, and the scene’s bigwig is no other than the lawyer Bill Shea, the eventual founder of the Mets. The scene captures the era with referential flair; Lenny decries Jackie Robinson’s conservatism, while Shea name-drops longtime baseball commissioner Ford Frick and New York mayor Robert Wagner, Jr. In an especially hilarious moment, the secretary suggests that if Lenny really wants to appeal to the “popular front” with his jingle, he should go for street-corner doo-wop as opposed to folk. Lenny agrees, commenting with deep stoicism on the “dialectical curveball” the secretary throws in his direction.

The above scene combines historical subtlety and mood with humorous glimpses into Lenny’s psyche. Simultaneously attempting to juggle Shea’s obvious disapproval of the Proletariats and his pathetically awkward flirtation with Shea’s secretary, Lenny struggles to remember the secretary’s name while pondering over how to avoid presenting the team as inherently Communist. Lethem, an understated yet effective reader, provided Lenny with a nervous New York accent, which he countered with Shea’s smooth lawyer voice. He pronounced his own astonishingly varied and complex vocabulary with ease, presenting detailed descriptions of hands, hems, and expressions. The futility of Lenny’s proposal, which ends with Shea announcing that he’d already secured the National League’s approval for the Mets, is both sardonic and somewhat heartbreaking. The scene represents well the novel’s intermingling of tragicomic character study and sociocultural analysis.

At the conclusion of the excerpt, Lethem opened up the house to a relaxed question-and-answer session. Candid and kind, Lethem revealed that he himself was a “red-diaper baby” (the child of Communist sympathizers) and had poured many autobiographical elements into his novel. The Angrush matriarch was loosely based on Lethem’s own grandmother. Yet the improvisation and spontaneity of fiction writing, Lethem said, led the character in a number of directions that deviated from those his grandmother took. Lethem jumped effortlessly through a wide range of topics, including his desire to mimic Dickensian reference to 1850s London in his largely New York-centric canon. Lenny’s otherworldly personality, Lethem also said, can be viewed as a replacement for his usual sci-fi elements that are lacking in “Dissident Gardens.”

Other audience queries had nothing to do with “Dissident Gardens.” Several questions focused on Lethem’s acclaimed 2003 novel “Fortress of Solitude,” leading the author to wax nostalgic on the “special place” he was in while writing the tome. Another audience member asked about Edward Norton’s long-delayed adaptation of “Motherless Brooklyn,” in response to which Lethem quipped that he was fine with whatever happened, having already received his compensation for the option.

Lethem ended the discussion with a brief polemic on the psychological complexity of “pure ideology.” Himself a believer in the necessity of ideological compromise and skepticism, Lethem wrote “Dissident Gardens,” and a bevy of his other work, partially as an examination of those who, like Lenny, believe completely in their respective causes. His philosophical concerns evidently have remained constant through his switch in genres. His latest novel’s grounding in the natural world may be a departure from much of his previous writing, but in “Dissident Gardens,” Lethem’s ideological explorations will once again find a home through his emotional honesty and deep knowledge of traits of the past.