Seven-year-old Wen and her parents, Eric and Andrew, are vacationing at a remote cabin on a quiet New Hampshire lake. Their closest neighbors are more than two miles in either direction along a rutted dirt road.

One afternoon, as Wen catches grasshoppers in the front yard, a stranger unexpectedly appears in the driveway. Leonard is the largest man Wen has ever seen but he is young, friendly, and he wins her over almost instantly. Leonard and Wen talk and play until Leonard abruptly apologizes and tells Wen, "None of what’s going to happen is your fault". Three more strangers then arrive at the cabin carrying unidentifiable, menacing objects. As Wen sprints inside to warn her parents, Leonard calls out: "Your dads won’t want to let us in, Wen. But they have to. We need your help to save the world."

(From Goodreads)