‘Very funny, my dear Aunt Jane,’ Raymond said gently, ‘but surely that has nothing to do with the very interesting story that Mr Petherick has been telling us.’

‘Oh yes, it has,’ said Miss Marple. ‘It is a catch! And so is Mr Petherick’s story a catch. So like a lawyer! Ah, my dear old friend!’ She shook a reproving head at him.

‘I wonder if you really know,’ said the lawyer with a twinkle.

Miss Marple wrote a few words on a piece of paper, folded them up and passed them across to him.

Mr Petherick unfolded the paper, read what was written on it and looked across at her appreciatively.

‘My dear friend,’ he said, ‘is there anything you do not know?’

‘I knew that as a child,’ said Miss Marple. ‘Played with it too.’

‘I feel rather out of this,’ said Sir Henry. ‘I feel sure that Mr Petherick has some clever legal legerdemain up his sleeve.’

‘Not at all,’ said Mr Petherick. ‘Not at all. It is a perfectly fair straightforward proposition. You must not pay any attention to Miss Marple. She has her own way of looking at things.’

‘We should be able to arrive at the truth,’ said Raymond West a trifle vexedly. ‘The facts certainly seem plain enough. Five persons actually touched that envelope. The Spraggs clearly could have meddled with it but equally clearly they did not do so. There remains the other three. Now, when one sees the marvellous ways that conjurers have of doing a thing before one’s eyes, it seems to me that the paper could have been extracted and another substituted by George Clode during the time he was carrying the overcoat to the far end of the room.’

‘Well, I think it was the girl,’ said Joyce. ‘I think the housemaid ran down and told her what was happening and she got hold of another blue envelope and just substituted the one for the other.’

Sir Henry shook his head. ‘I disagree with you both,’ he said slowly. ‘These sort of things are done by conjurers, and they are done on the stage and in novels, but I think they would be impossible to do in real life, especially under the shrewd eyes of a man like my friend Mr Petherick here. But I have an idea—it is only an idea and nothing more. We know that Professor Longman had just been down for a visit and that he said very little. It is only reasonable to suppose that the Spraggs may have been very anxious as to the result of that visit. If Simon Clode did not take them into his confidence, which is quite probable, they may have viewed his sending for Mr Petherick from quite another angle. They may have believed that Mr Clode had already made a will which benefited Eurydice Spragg and that this new one might be made for the express purpose of cutting her out as a result of Professor Longman’s revelations, or alternatively, as you lawyers say, Philip Garrod had impressed on his uncle the claims of his own flesh and blood. In that case, suppose Mrs Spragg prepared to effect a substitution. This she does, but Mr Petherick coming in at an unfortunate moment she had no time to read the real document and hastily destroys it by fire in case the lawyer should discover his loss.’