'Cheer up, Poirot; you know you are unique in your own line.'

'But what is there on hand in my own line?'

I picked up the paper.

'Here's an Englishman mysteriously done to death in Holland,' I said.

'They always say that - and later they find that he ate the tinned fish and that his death is perfectly natural.'

'Well, if you're determined to grouse!'

'Tiens!' said Poirot, who had strolled across to the window. 'Here in the street is what they call in novels a "heavily veiled lady". She mounts the steps; she rings the bell - she comes to consult us. Here is a possibility of something interesting. When one is as young and pretty as that one, one does not veil the face except for a big affair.'

A minute later our visitor was ushered in. As Poirot had said, she was indeed heavily veiled. It was impossible to distinguish her features until she raised her veil of black Spanish lace. Then I saw that Poirot's intuition had been right; the lady was extremely pretty, with fair hair and large blue eyes. From the costly simplicity of her attire, I deduced at once that she belonged to the upper strata of society.

'Monsieur Poirot,' said the lady in a soft, musical voice, 'I am in great trouble. I can hardly believe that you can help me, but I have heard such wonderful things of you that I come literally as a last hope to beg you to do the impossible.'

'The impossible, it pleases me always,' said Poirot. 'Continue, I beg of you, mademoiselle.'

Our fair guest hesitated.

'But you must be frank,' added Poirot. 'You must not leave me in the dark on any point.'

'I will trust you,' said the girl suddenly. 'You have heard of Lady Millicent Castle Vaughan?'

I looked up with keen interest. The announcement of Lady Millicent's engagement to the young Duke of Southshire had appeared a few days previously. She was, I knew, the fifth daughter of an impecunious Irish peer, and the Duke of Southshire was one of the best matches in England.

'I am Lady Millicent,' continued the girl. 'You may have read of my engagement. I should be one of the happiest girls alive; but oh, M. Poirot, I am in terrible trouble! There is a man, a horrible man - his name is Lavington; and he - I hardly know how to tell you. There was a letter I wrote - I was only sixteen at the time; and he - he -'

'A letter that you wrote to this Mr Lavington?'

'Oh no - not to him! To a young soldier - I was very fond of him - he was killed in the war.'

'I understand,' said Poirot kindly.

'It was a foolish letter, an indiscreet letter, but indeed, M. Poirot, nothing more. But there are phrases in it which - which might bear a different interpretation.'

'I see,' said Poirot. 'And this letter has come into the possession of Mr Lavington?'