I hurried to the window. True enough, there he was, tearing down the street, hatless, and gesticulating as he went. I turned to Mary with a gesture of despair.
"He'll be stopped by a policeman in another minute. There he goes, round the corner!"
Our eyes met, and we stared helplessly at one another.
"What can be the matter?"
I shook my head.
"I don't know. He was building card houses, when suddenly he said he had an idea, and rushed off as you saw."
"Well," said Mary, "I expect he will be back before dinner."
But night fell, and Poirot had not returned.