The Adventure of the Mad Tea Party

Ellery and his agent, Howard Biggers, travel to the estate of the wealthy and eccentric Spencer Lockridge. It seems as though Biggers wants to turn one of Ellery's books into a play and is trying to get Lockridge to provide the financial backing. All goes for naught when Lockridge disappears while wearing a Mad Hatter's costume from the Alice in Wonderland theme party he was throwing. Whodunit? Could it have been someone from New York or maybe even Dallas?