Evil Under the Sun

Colonel Weston asked:
‘Redfern’s wife is one of them, I suppose?’
‘Yes. Mrs Redfern might have made up her mind to kill Arlena Stuart. She had, let us say, ample cause. I think, too, that it would be possible for Mrs Redfern to commit a murder. But not this kind of murder. For all her unhappiness and jealousy, she is not, I should say, a woman of strong passions. In love, she would be devoted and loyal-not passionate. As I said just now-arsenic in the teacup, possibly-strangulation, no. I am sure, also, that she is physically incapable of committing this crime, her hands and feet are small, below the average.’
Weston nodded. He said: 
‘This isn’t a woman’s crime. No, a man did this.’
Inspector Colgate coughed.
‘Let me put forward a solution, sir. Say that prior to meeting this Mr Redfern the lady had had another affair with someone-call him X. She turns X down for Mr Redfern. X is mad with rage and jealousy. He follows her down here, stays somewhere in the neighbourhood, comes over to the island, does her in. It’s a possibility!’
Weston said:
‘It’spossible, all right. And if it’s true, it ought to be easy to prove. Did he come on foot or in a boat? The latter seems more likely. If so, he must have hired a boat somewhere. You’d better make inquiries.’
He looked across at Poirot.
‘What do you think of Colgate’s suggestion?’
Poirot said slowly:
‘It leaves, somehow, too much to chance. And besides-somewhere the picture is not true. I cannot, you see, imagine this man…the man who is mad with rage and jealousy.’
Colgate said:
‘Peopledid go potty about her, though, sir. Look at Redfern.’
‘Yes, yes…But all the same-’
Colgate looked at him questioningly. 
Poirot shook his head.
He said, frowning:
‘Somewhere, there is something that we have missed…’