While Grin's scientist father is disturbed by the unexplained disappearance of his research institute's director, Magnus G. Musselman, Grin is more interested in emulating his father and sets his mind to conducting a series of crazy experiments: on flies. He cannot imagine the trouble this will land him in. Literally cut down to size when he is faced down by a big fat bluebottle, he finds himself prey to a gigantic wasp and is only saved at the last minute by a huge frog that takes pity on him when he lands on a lily pad in the garden pond. Guiding Grin down through the depths of this pond, the frog takes him to a fabulously weird world called Quilibria with the promise of a quick fix for his situation. Yet the fix is not as quick as he would hope in this strange new dimension, where nothing is quite what it seems.

But it is the only place where Grin can hope to find the solution to his sadly shrunken state and get back to his normal size. As he travels through Quilibria in search of the solution, he is met with one obstacle after another thrown in his way by a succession of weird creatures.

Will he find what he's looking for? If he does, will he be able to take it with him or will he stay this size forever? And what does Magnus G. Musselman's disappearance have to do with any of this?