Huckle and the gang race all over Busytown trying to find the lock that fits an old key they found. They search everywhere from the Busytown Museum to Mr Gronkle's antiques. They come up empty until they remember that an old roll top desk was being delivered to the antique store near where they found the key and had a lock on it. They try the key and it fits. Lowly discovers chocolate sauce dripping down from his apple car roof. No one can figure out how it got there. When the kids encounter a taxi with the same gooey problem, they learn that both vehicles have recently been through the car wash. Further investigation leads them to the problem - a delivery truck lost one of its chocolate sauce bottles in the car wash's polishing brush.