The Secret Box; The Shrinking Dragon

Corky goes to town and brings back a box. She tells Bill that there's nothing in it but she won't show him the insides. But if there's nothing in it, why is it such a big secret? / A jewel from Rumble's dragon treasure is missing. Bill and Corky think that Rumble has so much treasure that he won't miss it. But Rumble does miss it - for if a dragon loses any treasure, he begins to shrink.