Greta is a girl on a mission: to venture to Avalon and bring back a hero who can save her home from destruction by the monstrous giant Yuk. 
Many heroes have tried before now. Many have failed.
What Greta needs is a hero whose courage and self-belief are greater than himself. She needs Hercufleas.
The only problem: he is a flea, no bigger than a raisin. But the smallest person might just have the biggest effect . . .