From Amazon.co.uk:
King Bendigo is the wealthiest man alive. He has an enormous security detail on his private island, quite capable of dealing with international aggression. But not threats from within his own family. Fearing for his life, he hires brilliant detective Ellery Queen.

The King's brother Judah makes no secret of wanting him dead. He even gives a date and a time on which he will commit the crime. So when the day comes, the King is kept in a hermetically sealed room while his brother is guarded by Ellery himself.

But the King is still shot...

An old Penguin edition published in 1960.

Left at the Street Library.

Release #13 for the 2019 Royalty Challenge.