“No, no, my friend,” he declared. “I do well to be careful. Do not forget the Big Four are on our track.”

However, he soon elicited the information that a nurse of the name of Mabel Palmer was a member of the Lark Institute and had been sent to the case in question.

“So far, so good,” he said, with a twinkle. “And now here comes Nurse Palmer back again, and here also is our analyst’s report.

“Is there arsenic in it?” she asked breathlessly.

Poirot shook his head, refolding the paper.

“No.”

We were both immeasurably surprised.

“There is no arsenic in it,” continued Poirot. “But there is antimony, and that being the case, we will start immediately for Hertfordshire. Pray Heaven that we are not too late.”