The Blossoms and the Green Phantom — Betsy Byars / Betsy Cromer Byars

Junior Blossom has finally created the ultimate invention -- the Green Phantom. It's big, black, Day-Glo green, and it's beautiful! All it needs is the secret ingredient.

The whole family makes a promise to ensure that Junior's invention will be a success, a Blossom promise that can never be broken.

Family and friends gather to launch the Green Phantom, but where are Pap and his dog, Mud? They wouldn't break a Blossom promise unless they were in serious trouble....