As Ms. Fash recalls in Lifeguard: A Love Story she was placed at the most dangerous post, Rockaway Beach in Queens ... Conveys the rowdy atmosphere of her early years on the job ... A third of the way into the narrative, Ms. Fash turns her attention to Peter Stein—who for years held the city’s top lifeguard position ... The shift is slightly jarring, akin to settling in for an episode of Baywatch and suddenly finding yourself watching On the Waterfront ... Yet Lifeguard, true to its subtitle, pays as much attention to the magic of the beach as its dangers.