I can just picture the cousins arguing with the editor of This Week over the title of this short story. The sensational title “Terror in a Penthouse” is the one they went with, while “No Parking” is a little more relevant and amusing.
Ellery suspects the possibility of foul play, and drives quickly to the scene of the possible crime. He can find no place to park. He drives around the block several times before using a quasi-legal space. Rushing to the apartment, he finds that he is minutes late, that the inability to park made him too late to stop the crime. And I can picture one of the cousins coming up with the idea for this story after a similar, frustrating experience on the streets of New York.
One other interesting part of this story is that while there are the usual three suspects, the guilty party lies outside of that box. And yes, Ellery does receive a parking ticket for his troubles.