This is book 46 of the "Nero Wolfe" series.

This note contains spoilers for the book.

Described on the cover as "his last case". That's compatible with the copyright date.

This is the one where a waiter at Rusterman's finds out something he shouldn't, and gets killed for it. As does his daughter, and a prominent electronics businessman.

I noticed an actual brand name in this book. In fact two of them—Coke, and Myers rum. Mentioned together, even.