At 5:26 Inspector Queen says to Ellery "... if you have a few minutes before you take off for Wrightsville...". Thus we learn that Ellery's cabin is in the same town featured in "The Adventure of the Chinese Dog".
Ellery mentions he's going to Wrightsville to the family cabin to write. Wrightsville is the small upstate New York town where "The Adventure of the Chinese Dog" was set.
When Ellery meets Zelda Van Dyke in her apartment, Arthur Van Dyke, her grandson who writes obituaries for the newspaper states that Ellery was born in NYC on April 2, 1912. Since the show is set in 1947, this would indicate that Ellery is 35 years of age. Actor Jim Hutton was 41 at the time.
In this episode Ellery has a brown tweed hat. He usually wears a gray tweed hat.
Actor John Finnegan, who plays Fred, the elevator operator, also played Cleary, the bartender who testifies in court in the pilot, "Too Many Suspects". He also made frequent appearances on other Levinson & Link shows, such as "Murder She Wrote" and "Columbo" as a variety of characters.