Ivy is the beloved houseplant of young Jillian Tupper of Number 3 Ramshorn Drive, much to the constant dismay of Toasty the goldfish, who is technically the family pet--swimming in his special place of honor, the antique octagonal fish tank--and should be the most loved. It seems that's how the cookie (or cheese puffs, in Toasty's case) crumbles in the curious Tupper household, but soon a sequence of thrilling and magical events challenges that way of life forever.

First, there's the arrival of Arthur, a knowledgeable spider with a broken leg and a curious mind, hidden in an old typewriter. Then Jillian throws everyone for a loop when she brings home dear, sweet Ollie, a school houseplant who just wants to be friends and sing. When Toasty splashes the plants with his tank water out of frustration, the friends learn that they can do magical things--like lift heavy objects and turn things invisible!

It turns out Toasty's fishtank isn't just for fish; it was made by a curious inventor who gave it special powers that, in the wrong hands, could disrupt everything forever. And a curious man with purple shoes just so happens to want that tank at any cost. Can Ivy, Toasty, Arthur, and Ollie grow to be friends in time to work together to save their beloved Tupper family from utter ruin?