The Castle of Mystery

Four children, an enthusiastic Jennifer, little Eddy, caring Daisy and eldest of the lot, Mason, get curious about the Bat Castle on Poppy Hill. At their Aunt's place, they discover an eye-catching Clock Tower. They long to explore them, that they do, but only by running into an adventure. What do they find out at The Clock Tower? Is that the end of the adventure or the beginning of a new one?