Quick recap
Marco's mom is afraid of everything and won't let him play softball. He sneaks off to a game, and Gwynnie hits him with a bat. At home, a phone that isn't there rings, and a boy named Keith says he lives in the basement and needs Marco to take care of him. Keith appears in his room and vanishes, a doctor wants to remove Marco's brain, and Gwynnie turns inside out in front of him. Keith becomes a yellow blob clinging to him. The twist: Keith, a monster, is the one who got hit, and it was all his nightmare. His mom warns that Marco and Gwynnie, the humans upstairs, must never find out monsters live in the basement. Just then, Marco walks down the stairs.
No spoilersOpens once you mark the title as seen.