The Man in the Queue question

I had not read The Man in the Queue for many years and my initial reaction in a re- reading was disappointment because Tey seemed to show so many of the expected prejudices of her time - hence the murder was committed by a man of the Levant! "No thorough Englishman used such a weapon."
And indeed they did not. but not in the way Grant' assumes and not in the way a modern reader might suppose either. And so Tey confounds our biases and even after all these years triumphs.