This book is a turny, twisty ride, with plot developments you never see coming, but are enjoyable if you just hold on and keep reading.
Rory is bullied at school, mostly by Tommy-Lee Komissky, who he nicknames "Grim" because, well, that's what the boy makes life -- grim, every time he throws Rory off the bus or steals his lunch or punches him in the school corridors.
Grim disappears for two weeks, two of the best weeks at school Rory's ever had.
Until Rory turns green. Not avocado green, or split-pea green, or evergreen green -- but broccoli green. Bright and healthy green.
Rory's whisked off to the hospital and put in quarantine (which he'd kinda enjoy, actually), only to discover the lump in the corner of the room is...a very green Grim.
Grim beats up Rory. But that night, when Grim's sleeping, he sleepwalks -- punching codes into secured doors, all while in his sleep -- and Rory follows. Except Grim goes to the roof and steps off -- whereupon Rory discovers he has heretofore undiscovered supernatural powers of super-speed / flying (but only for very short distances -- very short), and he "saves" Grim when they land in the window washer's cage.
Before they know it, Grim and Rory aren't friends, exactly, but they're coordinating to try to escape quarantine, which they manage to do and pick up a third green kid, this time a girl, and a penguin, and smuggle them back into quarantine (now their "secret lair"), to some real consternation on the part of their nurse.
I won't spoil how it ends; even if I detailed all the plot twists, you'd never see it coming. What a wonderful read!