With a nod both to the legion of series collectors and my own childhood memories:
Robert Arthur's Alfred Hitchcock and The Three Investigators and the Secret of Terror Castle. NY: Random House, 1964. Issued without a dust jacket. This is the first book written in The Three Investigator's juvenile mystery series.
(I loved this series as a kid and judging from the large number of fan sites I'm not the only one who remembers it fondly.)