Four cousins, all with the last name York, each live in an individual little "castle" in New York City, in York Square, which surrounds York Park. Two of the cousins are male, one a stiff and proper stamp collector, the other a ne'er-do-well idler. Two are women, a dedicated social worker, and a woman who seems to have some cognitive disability, reminding me of the White Queen in Alice in Wonderland. The cousins are all in or around their forties. They live in these castles in response to their uncle's will, leaving them significant fortunes if they remain living there until a certain time has passed. As the book begins, their inheritance is only a few months away.
Also living in the castles are a handyman, a secretary-assistant to the stamp collector, and a companion to the impaired woman. A housekeeper is shared by the two male cousins.
And then the murders start.
The police officer in charge of the case is Inspector Richard Queen, who hopes to tempt his son Ellery, an author and highly successful amateur detective, out of his torpor by involving him in the case. Eventually it seems that not only the Queens but half the New York City Police Department are working on the case, but more people from York Square are killed. The reader knows early on who is committing the murders and that that person is doing so at the behest of someone whose identity remains hidden.
The name of the author of most of the "Ellery Queen" mysteries was given as also being Ellery Queen. It was not a secret that "Ellery Queen" was really two people, Manfred B. Lee and Frederic Dannay. What was a secret was that some of the later books in the series were written, wholly or in part, by ghost writers using the Ellery Queen name. Multiple sources on the internet say that The Player on the Other Side was largely written by Theodore Sturgeon, known principally as a science fiction author.
Sturgeon was renowned for the beauty of his prose, but that is not generally apparent here. Still, there are places where the readers can see Sturgeon shining through. The following paragraph feels to me like Sturgeon's work:
"I was thinking of Percival," Ann said earnestly. "He's come so far. It's been fascinating to watch - how he pushed himself into this, into a work discipline, a hard schedule, regular meals and sleep. And suddenly you could see him light up as if two wires had touched to complete a circuit. Stamps stopped being what he used to call 'nothing.' Now he holds a stamp with his tongs and it isn't colored paper to him any more. It's a messenger of ideas and feelings between people as well as history and geography and politics and so many other things. You know, for a while Perce was angry? In a how-long-has-this-been-going-on way? Ellery, I don't want him hurt. It's too soon. He's too - too new."
I have read quite a few Ellery Queen short stories but only a couple of the novels, so I can't really compare this book to Queen's works as a whole. The Player on the Other Side is the only Ellery Queen book to be nominated for a "Best Novel" Edgar Award. (I would imagine that Manfred B. Lee and Frederic Dannay must have been both honored and irritated that an "Ellery Queen" book that they did not actually write was the one recognized by their peers from the Mystery Writers of America. I wonder if the MWA members who voted for The Player on the Other Side were aware of this situation.)
I can explain one reference that might puzzle readers who were not listening to the radio in the 1940s. The passage says, "Not since that magnificent miser, Jack Benny, was asked by a holdup man, 'Your money or your life,' had a man seemed in such anguished indecision as Percival York."
Jack Benny was a comedian who was famous on radio and television and in films in the 1930s - 1970s. Part of his comedy persona was his extreme parsimony. On his radio show of March 28, 1948, there was a sequence in which Benny was held up:
Mugger: Don't make a move, this is a stickup! Now come on! Your money or your life!
[long pause]
Mugger: Look, Bud, I said your money or your life.
Benny: I'm thinking it over!
[followed by what is reputed to be the longest burst of laughter in radio history]
And none of this has much to do with The Player on the Other Side. I think that this is a reasonably good mystery but not a truly outstanding one. It is certainly not as good a novel as some of Theodore Sturgeon's other works, such as More Than Human, The Dreaming Jewels, or Some of Your Blood. I correctly guessed the murderer shortly before it was revealed, but that really was a guess, not a deduction. I did not guess the explanation, withheld until the end of the book, of why the dog was named Beelzebub, a fine mystery in itself.