What is the underlying theme of 'The Catbird Seat' by James Thurber?

The surprise is that Mrs. Barrows is still alive at the end of the story when everyone in the story and reading it, except for Mrs. Barrows, wants to see her wearing a wooden kimono.

Perhaps a better test question type answer would be that the meek mild Mr. Martin, having failed to carry out his intended murder, never the less prevails over the strong willed domineering Mrs. Barrows by deftly changing his plan. He does and says things so out of character and so outlandish that when Mrs. Barrows reports all to Mr. Fitweiler the next day, she is immediately fired and hauled bodily from the office for being insane. This use of brains against brawn, succeeds in Mr. Martin now being as free of Mrs. Barrows as if he had actually gone through with the planned murder.