I found him installed in one of the newest type of service flats in London. I accused him (and he admitted the fact) of having chosen this particular building entirely on account of its strictly geometrical appearance and proportions.

‘But yes, my friend, it is of a most pleasing symmetry, do you not find it so?’

I said that I thought there could be too much squareness and, alluding to an old joke, I asked if in this super-modern hostelry they managed to induce hens to lay square eggs.

Poirot laughed heartily.

‘Ah, you remember that? Alas! no—science has not yet induced the hens to conform to modern tastes, they still lay eggs of different sizes and colours!’

I examined my old friend with an affectionate eye. He was looking wonderfully well—hardly a day older than when I had last seen him.

‘You’re looking in fine fettle, Poirot,’ I said. ‘You’ve hardly aged at all. In fact, if it were possible, I should say that you had fewer grey hairs than when I saw you last.’

Poirot beamed on me.

‘And why is that not possible? It is quite true.’

‘Do you mean your hair is turning from grey to black instead of from black to grey?’

‘Precisely.’

‘But surely that’s a scientific impossibility!’

‘Not at all.’

‘But that’s very extraordinary. It seems against nature.’

‘As usual, Hastings, you have the beautiful and unsuspicious mind. Years do not change that in you! You perceive a fact and mention the solution of it in the same breath without noticing that you are doing so!’

I stared at him, puzzled.

Without a word he walked into his bedroom and returned with a bottle in his hand which he handed to me.

I took it, for the moment uncomprehending.

It bore the words:

Revivit.—To bring back the natural tone of the hair. Revivit is not a dye. In five shades, Ash, Chestnut, Titian, Brown, Black.

‘Poirot,’ I cried. ‘You have dyed your hair!’

‘Ah, the comprehension comes to you!’

‘So that’s why your hair looks so much blacker than it did last time I was back.’

‘Exactly.’

‘Dear me,’ I said, recovering from the shock. ‘I suppose next time I come home I shall find you wearing false moustaches—or are you doing so now?’

Poirot winced. His moustaches had always been his sensitive point. He was inordinately proud of them. My words touched him on the raw.

‘No, no, indeed, mon ami. That day, I pray the good God, is still far off. The false moustache! Quel horreur!’

He tugged at them vigorously to assure me of their genuine character.

‘Well, they are very luxuriant still,’ I said.

‘N’est ce pas? Never, in the whole of London, have I seen a pair of moustaches to equal mine.’

A good job too, I thought privately. But I would not for the world have hurt Poirot’s feelings by saying so.

Instead I asked if he still practised his profession on occasion.

‘I know,’ I said, ‘that you actually retired years ago—’