There have only been a few Poirot books where it is made very clear how much Poirot owes to the Sherlock Holmes stories. Poirot very much stands as his own character and as its own series. But when Dame Agatha does pay respects to the Holmes canon she does it without trying to write pastiche and without trying to hide their influence on her own work, and I applaud her for it!
‘Of course not, of course not,’ said Poirot. He waved me to a chair and offered me some tisane, which I instantly refused.
George entered at the apposite moment with a whisky decanter, a glass and a siphon which he placed at my elbow.
‘And what are you doing with yourself these days?’ I asked Poirot. Casting a look at the various books around him I said: ‘It looks as though you are doing a little research?’ Poirot sighed. ‘You may call it that. Yes, perhaps in a way it is true. Lately I have felt very badly the need for a problem. It does not matter, I said to myself, what the problem is. It can be like the good Sherlock Holmes, the depth at which the parsley has sunk in the butter. All that matters is that there should be a problem. It is not the muscles I need to exercise, you see, it is the cells of the brain.’
‘Just a question of keeping fit. I understand.’
‘As you say.’ He sighed. ‘But problems, mon cher, are not so easy to come by. It is true that last Thursday one presented itself to me. The unwarranted appearance of three pieces of dried orange peel in my umbrella stand. How did they come there? How could they have come there? I do not eat oranges myself. George would never put old pieces of orange peel in the umbrella stand. Nor is a visitor likely to bring with him three pieces of orange peel. Yes, it was quite a problem.’
I even felt a little emotional when Poirot muses about Arthur Conan Doyle and remembers his very own "Watson":
‘And then—there are always the old favourites.’
Again he dived for a book. ‘The Adventures of Sherlock Holmes,’ he murmured lovingly, and even uttered reverently the one word, ‘Maître!’
‘Sherlock Holmes?’ I asked.
‘Ah, non, non, not Sherlock Holmes! It is the author, Sir Arthur Conan Doyle, that I salute. These tales of Sherlock Holmes are in reality far-fetched, full of fallacies and most artificially contrived. But the art of the writing—ah, that is entirely different. The pleasure of the language, the creation above all of that magnificent character, Dr Watson. Ah, that was indeed a triumph.’
He sighed and shook his head and murmured, obviously by a natural association of ideas: ‘Ce cher Hastings. My friend Hastings of whom you have often heard me speak. It is a long time since I have had news of him. What an absurdity to go and bury oneself in South America, where they are always having revolutions.’
And, damn, I just love when Dame Agatha reveals some of her own process through the character of Ariadne Oliver, even when she's only mentioned in the Poirot universe:
‘I have read also,’ he said, ‘some of the early works of Mrs Ariadne Oliver. She is by way of being a friend of mine, and of yours, I think. I do not wholly approve of her works, mind you. The happenings in them are highly improbable. The long arm of coincidence is far too freely employed. And, being young at the time, she was foolish enough to make her detective a Finn, and it is clear that she knows nothing about Finns or Finland except possibly the works of Sibelius. Still, she has an original habit of mind, she makes an occasional shrewd deduction, and of later years she has learnt a good deal about things which she did not know before. Police procedure for instance. She is also now a little more reliable on the subject of firearms. What was even more needed, she has possibly acquired a solicitor or a barrister friend who has put her right on certain points of the law.’
The mystery in this story is not taking a backseat exactly, but it appears there is more to this book by way of adding flesh to the series than focusing only on solving the puzzle of the original story.