In 1980s suburban America, single mother Susan buys her son Lucas the best present a boy could want for his 8th birthday: WORMIES, a growable pet for kids akin to Sea Monkeys, that’s the hottest new release in toy stores across the country.

Since tragedy struck their family a year prior, Susan’s relationship with her teenage daughter Heather has been strained and tense, but Susan, Heather, and Lucas are forced to work together when something goes wrong with the growth process of Lucas’ new toy, and the animal mutates into a terrifying monster.