Lauren Groff’s first book was a wonder and a delight. “The Monsters of Templeton,” it was called, and it was funny, magnetic and clear-eyed in its wise portrayal of a young woman trying (and failing) to outrun her mistakes.

What a happy relief to discover Groff’s second novel is even better. Not every young writer lives up to the promise of a first book, but Groff has exceeded expectations.

A riveting chronicle of the rise and fall of an upstate New York commune as seen through the eyes of Ridley “Bit” Sorrel Stone — you could guess his parents were hippies even without the telltale use of the word “commune” — “Arcadia” is a vivid portrait of an idealistic community undone by the things that undo us all: selfishness, hunger for power, lust for an ill-defined freedom and the very times in which we live. Groff also examines the way in which our childhoods shape us — and the way that self-image can be hard to shake even when we’re adults who should know better.

Bit’s self-image, you see, is grounded in being the “miracle baby,” born in a Volkswagen Camper outside Ridley, Wyo., when his parents, Abe and Hannah, were groupies trailing a charismatic folk singer named Handy across the country. Born too small but a survivor already, he’s the “littlest bit of a hippie ever made,” in the words of a grocer whose scale is used to weigh him (“three pounds exactly. The size of an itty-bitty butternut squash”).

Three years later the traveling band, its numbers swelling, lands in upstate New York on 600 acres signed over to Handy by an accolyte. Arcadia, Handy calls it. There, the community will create its utopia, raise its food and children and rebuild Arcadia House, a decaying mansion on the hill. They will hire out as workers or midwives or pot dealers as necessary and embrace all who want to join their group (you’re in as long as you can stomach a lot of soy cheese). They will be governed by few rules, the most important of which is that everyone must work.

Outwardly, “Arcadia” is the picture of a fair-minded if hardscrabble community, but “(t)here is, Bit knows, what happens on the surface, and there is what pulls beneath,” Groff writes, as, little by little, cracks emerge in this utopia. Hannah’s battles with depression leave Bit terrified and exhausted. His father suffers an accident. Too many new people arrive who don’t adhere to Arcadia’s standards — they just like the drugs and free love — and even Handy’s once-benign influence takes on an unwelcome edge.

The novel follows Bit’s life from childhood — he thinks of it as idyllic despite occasional tragedy — through the community’s downfall during his adolescence, when he falls for Handy’s troubled daughter, Helle. Lies, secrets and too many outsiders overwhelm Arcadia, and its end is ugly, full of bitterness and recrimination.

From there, the novel leaps ahead to Bit’s adulthood in the Outside. He has always worried about the Outside: “He knows the only weapons against the threat of the Outside are knowledge and words; when anxiety bubbles up under his thoughts, he has to say Hannah’s name a hundred times. … He has always thought he’d return to Arcadia after college and make his life there. Who doesn’t want a second chance at paradise?”

Curiously, Groff skimps on Bit’s transition from country-bred vegan hippie kid to urban teenage animal. Instead, she slaps the adult Bit, a photographer, into a disturbing, not-too-far-off future in which a pandemic threatens and the pull of Arcadia grows even stronger.

How does a man become his own person when he desperately needs to be part of something bigger? That’s the gnawing question of the novel, and Groff traces Bit’s journey toward the answer with compassion, awareness and gentle humor.

The adult Helle acts as a splash of cold water on Bit’s image of Arcadia: “I can’t believe you don’t remember. It was cold, Helle said. We were never warm. We never had enough to eat. We never had enough clothes. … Handy let me drink the acid Slap-Apple when I was like five. What kind of hallucinations does a 5-year-old have?”

Helle’s right. Our memories can betray us, but Groff reminds us: Bit is a survivor. And in the end, our dreams don’t always let us down.