Evil Under the Sun

‘Perhaps. But you wanted to come here becauseshe was going to be here.’
‘She? Who is she?’
‘Mrs Marshall. You-you’re infatuated with her.’
‘For God’s sake, Christine, don’t make a fool of yourself. It’s not like you to be jealous.’
His bluster was a little uncertain. He exaggerated it.
She said:
‘We’ve been so happy.’
‘Happy? Of course we’ve been happy! Weare happy. But we shan’t go on being happy if I can’t even speak to another woman without you kicking up a row.’
‘It’s not like that.’
‘Yes, it is. In marriage one has got to have-well-friendships with other people. This suspicious attitude is all wrong. I-I can’t speak to a pretty woman without your jumping to the conclusion that I’m in love with her-’ 
He stopped. He shrugged his shoulders.
Christine Redfern said:
‘Youare in love with her…’
‘Oh, don’t be a fool, Christine! I’ve-I’ve barely spoken to her.’
‘That’s not true.’
‘Don’t for goodness’ sake get into the habit of being jealous of every pretty woman we come across.’
Christine Redfern said:
‘She’s not just any pretty woman! She’s-she’sdifferent! She’s a bad lot! Yes, she is. She’ll do you harm, Patrick, please,give it up. Let’s go away from here.’
Patrick Redfern stuck out his chin mutinously. He looked, somehow, very young as he said defiantly:
‘Don’t be ridiculous, Christine. And-and don’t let’s quarrel about it.’
‘I don’t want to quarrel.’
‘Then behave like a reasonable human being. Come on, let’s go back to the hotel.’
He got up. There was a pause, then Christine Redfern got up too.
She said:
‘Very well…’
In the recess adjoining, on the seat there, Hercule Poirot sat and shook his head sorrowfully.
Some people might have scrupulously removed themselves from earshot of a private conversation. But not Hercule Poirot. He had no scruples of that kind.
‘Besides,’ as he explained to his friend Hastings at a later date, ‘it was a question of murder.’
Hastings said, staring:
‘But the murder hadn’t happened, then.’
Hercule Poirot sighed. He said:
‘But already,mon cher, it was very clearly indicated.’
‘Then why didn’t you stop it?’
And Hercule Poirot, with a sigh, said as he had said once before in Egypt, that if a person is determined to commit murder it is not easy to prevent them. He does not blame himself for what happened. It was, according to him, inevitable.