Marvin and Stuart get to sleep over at Nick Tuffle's house for Nick's birthday. They set out sleeping bags in the Tuffles' backyard. Stuart and Nick fall right to sleep, but Marvin tosses and turns. Then he hears a noise, and something glowing zooms over his head. Is it "really a flying birthday cake? Or something else? The next day, a very strange new kid shows up at school. . . .