The Big Four - Agatha Christie

I´m sorry, but I´m going to quote the crap out of this one.

 

"Aha!" said Poirot. "So it is like that, is it? And what do your friends suggest?"

"They suggest, monsieur, that you should employ your talents - your very considerable talents - in the detection of legitimate crime. Return to your avocations and solve the problems of London society Ladies"

 

What did Poirot actually do to pop up on the radar of a world-wide operating criminal organization? All of a sudden they are at Poirots throat and vice versa.