The flying king of Kurio

In Michael and Amanda's New York apartment, there was a big closet in the back hall where the children had a shelf for their play things. One day, Michael noticed the back seemed to be loose, and when he gave it a push, it opened like a door. He began to explore the hall behind the closet and soon asked Amanda to join him. They found a door with a doorbell, and a card which read: Mr. and Mrs. Tractable. Of course they pushed the doorbell; in the apartment behind the door, they met an odd couple in an unusual apartment, where few of the walls were straight, a room was ready for them, and the mail was delivered by plane.