The Dragon Who Found a Monster Party: Dragon Who Series Volume 3 (Unabridged‪)‬

It's raining outside and Petey is bored. There is nothing to do. A noise escapes from his closet. What is it?

Petey goes to investigate and hears dancing music coming from inside. He opens up the door and finds stairs leading to a room below. Petey summons his courage and steps inside, but what will he find?