“Do you see?” he said.  “On the opposite side there are no houses; there is only a wall.  Behind the wall there are climbing gardens and the ground falls steeply to the turn of the road below.  There’s a flight of steps leading down which corresponds with the flight of steps from the garden.  Very often there’s a serjent-de-ville stationed on the top of the steps.  But there was not one there yesterday afternoon at three.  Behind us is the supporting wall of the hotel garden.  Well, look about you.  We cannot be seen from the hotel.  There’s not a soul in sight—­yes, there’s some one coming up the hill, but we have been standing here quite long enough for you to stab me and get back to your coffee on the verandah of the hotel.”

Ricardo started back.

“Marthe Gobin!” he cried.  “It was here, then?”

Hanaud nodded.

“When we returned from the station in your motor-car and went up to your rooms we passed Harry Wethermill sitting upon the verandah over the garden drinking his coffee.  He had the news then that Marthe Gobin was on her way.”

“But you had isolated the house in Geneva.  How could he have the news?” exclaimed Ricardo, whose brain was whirling.

“I had isolated the house from him, in the sense that he dared not communicate with his accomplices.  That is what you have to remember.  He could not even let them know that they must not communicate with him.  So he received a telegram.  It was carefully worded.  No doubt he had arranged the wording of any message with the care which was used in all the preparations.  It ran like this”—­and Hanaud took a scrap of paper from his pocket and read out from it a copy of the telegram:  “’Agent arrives Aix 3.7 to negotiate purchase of your patent.’  The telegram was handed in at Geneva station at 12.45, five minutes after the train had left which carried Marthe Gobin to Aix.  And more, it was handed in by a man strongly resembling Hippolyte Tace”—­that we know.”

“That was madness,” said Ricardo.

“But what else could they do over there in Geneva?  They did not know that Harry Wethermill was suspected.  Harry Wethermill had no idea of it himself.  But, even if they had known, they must take the risk.  Put yourself into their place for a moment.  They had seen my advertisement about Celie Harland in the Geneva paper.  Marthe Gobin, that busybody who was always watching her neighbours, was no doubt watched herself.  They see her leave the house, an unusual proceeding for her with her husband ill, as her own letter tells us.  Hippolyte follows her to the station, sees her take her ticket to Aix and mount into the train.  He must guess at once that she saw Celie Harland enter their house, that she is travelling to Aix with the information of her whereabouts.  At all costs she must be prevented from giving that information.  At all risks, therefore, the warning telegram must be sent to Harry Wethermill.”

Ricardo recognised the force of the argument.