A fourteen-year-old babysitter and her young charge spend the summer visiting Boston's Public Garden where they find unexpected friendships and new adventures.

Enid Crowley can't stand her name. When she takes a summer job baby-sitting young Joshua W. Cameron IV, Enid decides it's time for a change: she calls herself Cynthia, and Joshua becomes Tom Terrific. Every day they're off to Boston's Public Garden to meet new people and find excitement.

It doesn't take long before Cynthia and Tom Terrific pair up with Hawk, the saxophone player, and the old bag lady and become involved in the wildest adventure the park has ever seen. Their project is top secret. Nothing can go wrong. Or can it?