Patricia Wall / New York Times News Service"The Vacationers," by Emma Straub

“The Vacationers” by Emma Straub (Riverhead Books, 292 pgs., $26.95)

Emma Straub’s bustling new novel is about a New York family’s two-week idyll in a house on the Spanish island of Mallorca. It’s also about a different kind of break: infidelity. The book is full of couples, and all of them have to cope with some kind of cheating during the course of the story. Even its youngest, most petulant character, a sharp-eyed teenager named Sylvia Post, has been betrayed by her high school boyfriend and rewarded with an Adonis of a Spanish tutor as compensation.

“The Vacationers” is a much more inviting book than Straub’s forced and overpraised period piece, “Laura Lamont’s Life in Pictures.” This new book has exceptional freshness for its stuck-in-a-summer-house genre. The male characters tend to be two-dimensional, but the story’s women are so well-drawn that they seem instantly familiar. Chief among these is the Post family matriarch, Franny, who writes about food and travel. Her daughter, Sylvia, sees Franny as Joan Didion with an appetite or Ruth Reichl with an attitude; either way, Franny holds the book together through nagging, cooking and sheer force of will.

Franny arrives in Mallorca in a troubled state. Sylvia, the younger of her two children, is about to head off to college, which will leave Franny “looking at Jim in the kitchen and wanting to plunge an ice pick in between his eyes.” Jim, the patriarch, has just executed the double whammy of having an affair with an intern and losing his job as the editor of a magazine as a consequence. His is the first unwanted vacation to crop up in the story.

Straub does an entertaining job of filling the house with mismatched characters, so that everything they do together is automatically absurd. Jim and Franny’s older child, Bobby, is a good-looking dope who has gotten involved in the bodybuilding culture of Miami. He’s also brought along Carmen, a personal trainer more than a decade his senior. This does not please Franny, who doesn’t know a deltoid from an Altoid and who is dismayed to realize that Carmen seldom knows what the Posts are talking about. Carmen’s physique-obsessed frame of reference involves protein powders; Jim, her polar opposite, has a style that recalls Cary Grant’s, with “high-waisted pants and a way of talking that was both flirtatious and belittling at the same time.”

We can be sure that Carmen is trouble when Franny stages an expedition to the Robert Graves house, and Carmen (“museums aren’t really my thing”) goes shopping for sequined tops instead.

But Straub builds interest into the question of just when and how things will go wrong. Jim is a proven lech, stuck in the boring bosom of his family; Carmen is a hot physical specimen who is constantly wandering into his line of view in her skintight exercise gear. Fortunately, “The Vacationers” never falls for plot tricks as obvious as that. And when its characters transgress, they do it in far more revealing ways.

The other couple in the mix are two visiting gay men: Charles, who is Franny’s best friend and confidant, and Lawrence, his much younger husband. Lawrence eagerly wants to adopt a baby, and he and Charles spend the two weeks on the verge of hearing that they have been chosen. Charles had been perfectly content doting on his friends’ babies, “pipsqueaks for whom he could buy expensive, dry-clean-only clothes and other impractical gifts.” Besides, he is a painter, and there’s no room in his life for child coddling. But Lawrence is even busier — he’s producing a werewolf movie, about which the book is very funny — and thoroughly determined. And yes, even these two have an episode of sexual betrayal to deal with before the book is over.

Straub writes some wonderful one-on-one scenes, as when the virginal Sylvia is finally left alone with her tutor, or when Franny and Charles lock themselves in a bathroom, she in the tub, to share the kinds of confidences that only friends of 40 years’ standing could. And some of the en masse scenes have an antic energy that keeps this book a cut above the ordinary. But at heart, “The Vacationers” is formulaic enough to insist that everyone emerge from its machinations as a better person, or at least a braver one. That means that, at some point, it parts ways with reality and turns into a sugarcoated fairy tale.

The story’s resolution of Jim and Franny’s troubles is its low point: convenient for the author but credible only to readers with amnesia. Straub’s spirit of forgiveness may be admirable, but it takes all the teeth out of what she has been building. Like so many rom-com movies with final half hours that must be suffered through, “The Vacationers” winds up realizing that everybody makes mistakes. A book witty enough to use a tennis pro’s name, Antoni, to set up an allusion to the mimes’ racquetless tennis scene in Michelangelo Antonioni’s 1966 “Blow-Up” is much too clever to play so dumb.