The blossoms and the green phantom

No one has noticed Junior Blossom's new invention even though Junior can plainly see that it's marvelous. He calls it the Green Phantom and it's almost finished except for the final secret ingredient. The whole family make a Blossom promise to ensure Junior's Green Phantom is a big success and Junior knows a blossom promise can never be broken. When the Green Phantom is ready everyone gathers to cheer Junior on except for two people: Pap his grandfather who has been missing  and Mom who is at home worried and waiting near the phone. Pap is old and his knees are weak where can he be?