In “Mathilde,” one of the two novellas that make up this book, a 24-year-old lives with twin sisters and works as a negative commenter on various websites. Her anonymous comments send site owners running to her brother-in-law to improve their web presence. When she loses a bag with 10,000 euros in it, she becomes obsessed with the unkempt man who finds and returns it. In “Yann,” a 26-year-old man happens into dinner with older married neighbors. Basking in their affection and repartee is “one of the most beautiful evenings of my unpromising existence,” and proves to him how hollow his own romantic relationship has been. Both stories have a sentimental streak, but Ms. Gavalda, a best-selling author in her native France, puts them across with charm. “You don’t meet the people you love,” the husband upstairs tells Yann, “you recognize them.”
