This note contains spoilers for the book.

The 17th Nero Wolfe book (two novellas).

Jumping quite a ways ahead; these are set during WWII, starting with Wolfe trying to get into shape to join the army and kill Germans, and Archie, a Major in military intelligence, being assigned to get him back to doing detective work for the army.

The secret observation panel in the office plays a key role in the second ("Booby Trap"). Also, the red chair appears. In fact, one day a character is told to take certain chair because it's the best one, and the next day there's a red leather chair in the office. And it stays there for the rest of the series, and the rest become green instead of nondescript.