COMMONWEALTH

By Ann Patchett

Harper, 336 pp., $27.99

It’s a fundamental fact about people in groups, large or small, intimately acquainted over a long period or thrown together for the afternoon: Present for the same events, no two people come away with identical experiences.

So on a Sunday in suburban Los Angeles sometime in the 1960s when a lawyer named Bert Cousins crashes a christening party for Fix and Beverly Keating’s second child — he didn’t know the Keatings, let alone their baby, when he arrived — he ends up having a vastly different day from his hosts, Fix in particular. Bert, who’d only gone to the party to avoid spending time with his pregnant wife, Teresa, and their three little kids, is convinced before he leaves that he must make Fix’s startlingly beautiful wife his own.

Lush, humane, and mischievously comical, Ann Patchett’s embraceable new novel, “Commonwealth,’’ is the half-century saga of the blended family that results from Bert’s success. When Beverly marries him — we know from the start that this is a bad idea, but Beverly is blithely unperturbed by his conspicuous selfishness and extreme fondness for guns — they move to Virginia, and she takes her daughters, Caroline and Franny, along.

Bert’s kids fly out from California to spend whole summers there in the kind of unstructured, unsupervised leisure that leaves them to make their own fun, and their own trouble. They are children, and their judgment of recklessness and danger is not at its most refined. True to the standard of the time, neither is that of their parents.

The combined brood gets along remarkably well, though it’s hardly “The Brady Bunch.’’ Albie, the youngest, grates on the bigger kids’s nerves, and they routinely feed him pills to conk him out while they proceed with their adventures.

Back in California, Fix, a police officer, and Teresa, who becomes a paralegal, remain part of the narrative — as does all the animosity, woundedness, and longing of bitter divorce and divided custody. Juggling work with hands-on parenting three seasons of the year, Teresa is overwhelmed. Fix, allowed to spend just one week every summer with his young daughters, mostly dotes from a distance, nursing his grudge against the stepfather who gets to watch them grow up.

“And what about old Bert? How’s he doing?’’ Fix asks Franny when he’s past 80, contentedly remarried, and a grandfather. “Do you talk to him very often?’’

“Not nearly as often as I talk to you,’’ Franny says.

“It isn’t a contest,’’ her father replies, though of course he’s the one who needs the reminder.

“Commonwealth’’ bounces backward and forward through the decades, a structure that helps sustain suspense. The novel’s central tragedy is the death of one of the children — an event whose details Patchett only gradually brings into focus. It’s a trauma understood and misunderstood from as many perspectives as there are family members. The kids, who were there that day, are too afraid to reveal certain facts to the grownups, who were not. No one has the whole story, just pieces. Grief and guilt walk through life with them.

For Franny, the character we know best in this well-populated ensemble, there is an additional reason for remorse, also related to that day. Drifting aimlessly after dropping out of law school, she’s waiting tables in a Chicago hotel bar the night she meets her idol, Leon Posen. Many years her senior, he is a famous author and dedicated drinker with a stalled career and a marriage on pause. She, young and lovely with an agile mind, is naturally flattered by his attention, and far too quick to sell herself short.

Franny falls in love with him, and in doing so she tells him the stories of herself. The one that most fascinates him is about her family: the divorces, Beverly and Bert’s marriage, the death. But that story doesn’t belong solely to her. As she knows while she’s doing it and regrets only later — after Leon gets back in the literary game by turning her family’s pain into an enormously successful novel — she has betrayed them by telling him.

Is it a spoiler to reveal that this does not break the family? It turns out that some real affection took root among those free-range kids.

That’s not to say that there are happy endings for everyone. Four parents, six kids, a little over 50 years: There’s going to be heartache, some of it permanent, and everyone finds a different way through. But for those who stick around in the family, there will also be redemption, even the mending of rifts. “This was the pleasure of a long life: the way some things worked themselves out.’’

COMMONWEALTH

By Ann Patchett

Harper, 336 pp., $27.99

Laura Collins-Hughes can be reached at laura.collinshughes @gmail.com.