“Sunburn” by Laura Lippman is about two loners, Polly and Adam, who meet in a sleepy Delaware not-quite-beach town. They begin an affair but each holds something back from the other— secrets that feed growing doubts about their motives. One is playing a long game. But which one? This is a “just-one-more chapter, stay-up-late suspense, but packed too with nuance [and] subtlety”(Lee Child).