The King Is Dead — Ellery Queen

Ellery Queen and his father discover a baffling murder on a private island

Ellery Queen and his father are meandering through breakfast when their apartment is invaded. Without making a sound, 2 men appear in the Queens' living room, guns drawn, and proceed to search the place. When they're done, a 3rd man follows: a paunchy little professor-type who happens to be the brother of a king. King Bendigo doesn't rule a country, but his control of the international arms trade has made him one of the richest men in the world. It's not surprising that somebody wants him dead.
 
Bendigo's brother comes to the Queens to ask them to save the tycoon's life -- but they fail. The king is found dead in a hermetically sealed room, a bullet lodged in his heart. The murder is impossible to solve -- that is, for anyone but Ellery Queen.