So, unless anyone knows the answer, I’m stuck pursuing guesses.

Carruthers is a character in “The Riddle of the Sands: A Record of Secret Service” , a 1903 thriller / espionage novel by Erskine Childers.

That was a best seller in its day, and could plausibly be the source. But the Project Gutenberg text doesn’t have the trope.

Perhaps it’s a line from an adaptation of the story, or a misquote?

Or perhaps this is a red herring?

https://en.m.wikipedia.org/wiki/The_Riddle_of_the_Sands

#TheRiddleOfTheSands
#ErskineChilders