“ Eh bien! Photo number three represents the highly magnified surface of a tiny bottle in the top poison cupboard of the dispensary in the Red Cross Hospital at Tadminster⁠—which sounds like the house that Jack built!”

“Good heavens!” I exclaimed. “But what were Lawrence Cavendish’s fingermarks doing on it? He never went near the poison cupboard the day we were there!”

“Oh, yes, he did!”

“Impossible! We were all together the whole time.”

Poirot shook his head.

“No, my friend, there was a moment when you were not all together. There was a moment when you could not have been all together, or it would not have been necessary to call to Monsieur Lawrence to come and join you on the balcony.”