Free Death in the Clouds by Agatha Christie

She’d have had to have knelt up in her seat and leaned over the top—with ten people looking at her. Oh, hell, let’s get on.’
    ‘9 and 10,’ said Fournier, moving his finger on the plan.
    ‘M. Hercule Poirot and Dr Bryant,’ said Japp. ‘What has M. Poirot to say for himself?’
    Poirot shook his head sadly.
    ‘ Mon estomac ,’ he said pathetically. ‘Alas, that the brain should be the servant of the stomach.’
    ‘I, too,’ said Fournier with sympathy. ‘In the air I do not feel well.’
    He closed his eyes and shook his head expressively.
    ‘Now then, Dr Bryant. What about Dr Bryant? Big bug in Harley Street. Not very likely to go to a French woman moneylender; but you never know. And if anyfunny business crops up with a doctor he’s done for life! Here’s where my scientific theory comes in. A man like Bryant, at the top of the tree, is in with all the medical research people. He could pinch a test-tube of snake venom as easy as winking when he happens to be in some swell laboratory.’
    ‘They check these things, my friend,’ objected Poirot. ‘It would not be just like plucking a buttercup in a meadow.’
    ‘Even if they do check ’em, a clever man could substitute something harmless. It could be done, simply because a man like Bryant would be above suspicion.’
    ‘There is much in what you say,’ agreed Fournier.
    ‘The only thing is, why did he draw attention to the thing? Why not say the woman died from heart failure—natural death?’
    Poirot coughed. The other two looked at him inquiringly.
    ‘I fancy,’ he said, ‘that that was the doctor’s first—well, shall we say impression? After all, it looked very like natural death, possibly as the result of a wasp sting; there was a wasp, remember—’
    ‘Not likely to forget that wasp,’ put in Japp. ‘You’re always harping on it.’
    ‘However,’ continued Poirot, ‘ I happened to notice the fatal thorn on the ground and picked it up. Once we had found that, everything pointed to murder.’
    ‘The thorn would be bound to be found anyway.’
    Poirot shook his head.
    ‘There is just a chance that the murderer might have been able to pick it up unobserved.’
    ‘Bryant?’
    ‘Bryant or another.’
    ‘H’m—rather risky.’
    Fournier disagreed.
    ‘You think so now,’ he said, ‘because you know that it is murder. But when a lady dies suddenly of heart failure, if a man is to drop his handkerchief and stoop to pick it up, who will notice the action or think twice about it?’
    ‘That’s true,’ agreed Japp. ‘Well, I fancy Bryant is definitely on the list of suspects. He could lean his head round the corner of his seat and do the blowpipe act—again diagonally across the car. But why nobody saw him—! However, I won’t go into that again. Whoever did it wasn’t seen!’
    ‘And for that, I fancy, there must be a reason,’ said Fournier. ‘A reason that, by all I have heard,’ he smiled, ‘will appeal to M. Poirot. I mean a psychological reason.’
    ‘Continue, my friend,’ said Poirot. ‘It is interesting what you say there.’
    ‘Supposing,’ said Fournier, ‘that when travelling in a train you were to pass a house in flames. Everyone’seyes would at once be drawn to the window. Everyone would have their attention fixed on a certain point. A man in such a moment might whip out a dagger and stab a man, and nobody would see him do it.’
    ‘That is true,’ said Poirot. ‘I remember a case in which I was concerned—a case of poison, where that very point arose. There was, as you call it, a psychological moment. If we discover that there was such a moment during the journey of the Prometheus —’
    ‘We ought to find that out by questioning the stewards and the passengers,’ said Japp.
    ‘True. But if there was such a psychological moment, it must follow logically that the cause of that moment must have originated with the murderer. He must have been able to produce the particular effect that caused