I opened it.
It was terse and to the point.
"You are wise," it ran.
It was signed with a big figure 4.
I could afford to smile to myself!
The sea was not too choppy.
I enjoyed a passable dinner, made up my mind as to the majority of my fellow passengers, and had a rubber or two of Bridge.
Then I turned in and slept like a log as I always do on board ship.
I was awakened by feeling myself persistently shaken.
Dazed and bewildered, I saw that one of the ship's officers was standing over me.
He gave a sigh of relief as I sat up.
"Thank the Lord I've got you awake at last.
I've had no end of a job.
Do you always sleep like that?"
"What's the matter?" I asked, still bewildered and not fully awake. "Is there anything wrong with the ship?"
"I expect you know what's the matter better than I do," he replied dryly. "Special instructions from the Admiralty.
There's a destroyer waiting to take you off."
"What?" I cried. "In mid-ocean?"
"It seems a most mysterious affair, but that's not my business.
They've sent a young fellow aboard who is to take your place, and we are all sworn to secrecy.
Will you get up and dress?"
Utterly unable to conceal my amazement I did as I was told.
A boat was lowered, and I was conveyed aboard the destroyer.
There I was received courteously, but got no further information.
The commander's instructions were to land me at a certain spot on the Belgian coast.
There his knowledge and responsibility ended.
The whole thing was like a dream.
The one idea I held to firmly was that all this must be part of Poirot's plan.
I must simply go forward blindly, trusting in my dead friend. I was duly landed at the spot indicated.
There a motor was waiting, and soon I was rapidly whirling along across the flat Flemish plains.
I slept that night at a small hotel in Brussels.
The next day we went on again.
The country became wooded and hilly.
I realised that we were penetrating into the Ardennes, and I suddenly remembered Poirot's saying that he had a brother who lived at Spa.
But we did not go to Spa itself.
We left the main road and wound into the leafy fastnesses of the hills, till we reached a little hamlet, and an isolated white villa high on the hill-side.
Here the car stopped in front of the green door of the villa.
The door opened as I alighted.
An elderly man-servant stood in the doorway bowing.
"M. le Capitaine Hastings?" he said in French. "Monsieur le Capitaine is expected.
If he will follow me."
He led the way across the hall, and flung open a door at the back, standing aside to let me pass in.
I blinked a little, for the room faced west and the afternoon sun was pouring in.
Then my vision cleared and I saw a figure waiting to welcome me with outstretched hands.
It was - oh, impossible, it couldn't be - but yes!
"Poirot!" I cried, and for once did not attempt to evade the embrace with which he overwhelmed me.
"But yes, but yes, it is indeed I!
Not so easy to kill Hercule Poirot!"
"But Poirot - why?"
"A ruse de guerre, my friend, a ruse de guerre.