Lillian and Madison were unlikely roommates and yet inseparable friends at their elite boarding school. But then Lillian had to leave the school unexpectedly in the wake of a scandal and they've barely spoken since. Until now, when Lillian gets a letter from Madison pleading for her help. Madison's twin stepkids are moving in with her family and she wants Lillian to be their caretaker. However, there's a catch: the twins spontaneously combust when they get agitated, flames igniting from their skin in a startling but beautiful way. Over the course of one humid, demanding summer, Lillian and the twins learn to trust each other - and stay cool - while also staying out of the way of Madison's buttoned-up politician husband. Surprised by her own ingenuity yet unused to the intense feelings of protectiveness she feels for them, Lillian ultimately begins to accept that she needs these strange children as much as they need her.