When the members of The Secret Knock Club learn that the spring fair will be without a dunk tank, they decide to raise money to rent a tank. Agnes, as usual, comes up with a Big Idea a rock band concert. She ll be the vocalist, the other club members will provide the music. But can Agnes sing? Do the others know how to play instruments? And what if Principle Not-Such-a-Joy s dog has an accident in the tank as he did the year before?"