He found it in The Murder on the Links, and he made that statement in Lord Edgware Dies.
In chapter 7 of Lord Edgware Dies, Poirot mentions this:
‘I found a clue once,’ said Poirot dreamily. ‘But since it was four feet long instead of four
centimetres no one would believe in it.’
This is in reference to The Murder on the Links, where a 4 ...
According to the Wikipedia page on Hercule Poirot and based on quotations from Curtain, Poirot died in October 1949, thirty-three years after he first met Captain Hastings in June 1916. (He wasn't actually retired by that point, but he was a refugee escaping from World War I: it's unclear when exactly he retired). We know that he was a detective with the ...
There's no need to read the Poirot books in any particular order.
Agatha Christie has rewritten a few of the early Poirot short stories (see list) from the book Poirot's Early Cases (1923) and The Regatta Mystery and Other Stories (1939) and the posthumous collection While the Light Lasts and Other Stories (1997) into full novels later. Thus, if you read ...
Whether Agatha Christie intentionally copied Watson in Hastings or not, he is an example of a necessity for a successful mystery writer: To fully engage a reader, generally one has to not just present the mystery and let the reader think about it to whatever extent he feels like doing and with whatever skill level he has. That route leads to dissatisfaction ...
As ShreevatsaR said:
The phrase you heard is Erin go Bragh, said by Irish Freedom sympathisers who kidnapped the Prime Minister.
The short story and the episode both go by the name: The Kidnapped Prime Minister. The short story is in the book Poirot Investigates.
This answer is largely based on the Movies & TV post which user1964 linked in a comment.
Yes, Poirot was a religious Catholic.
In the story Murder in Mesopotamia (Internet Archive link), he mentions twice that he is a "practising Catholic":
Then he said quite irrelevantly: ‘An interesting man, that Father Lavigny.’
‘A monk being an ...
TL;DR: It is not possible to put together a consistent biography of Poirot that includes all the stories.
Precise dates are very rare in the Poirot corpus, and there are few references to historical events that can be used to give a terminus post quem, but here is a selection of significant dates.
“I had a bad failure in Belgium in 1893. You ...