‘Moreover, I fancy she is very well aware that her son could anticipate his inheritance by borrowing upon his expectations and insuring his life as security for the loan. This reduces her motive to one of mere exasperation and the same may be said of Mr Bantling himself.’

‘And of me,’ said Bimbo quickly.

Alleyn said: ‘In your case there might well be something we haven’t yet winkled out. Which is what I mean about the secondary importance of motive. However, I was coming to you. You had ample opportunity. You retired to a bathroom where you tell me you spent a long time bandaging your hand. You could equally well have spent it driving back to the ditch and arranging the trap. No, please don’t interrupt. I know you were bitten. That proves nothing. You may also remember that you took Mr Leiss’s overcoat to him. Were his gloves in the pocket?’

‘How the hell do I know! I didn’t pick his ghastly pockets,’ said Bimbo, turning very white.

‘A statement that at the moment can’t be checked. All the same, there’s this to be said for you: if you are both telling the truth about your movements this evening, you are unlikely to have chucked the paper-weight at Mr Period’s head. Although,’ Alleyn said very coolly, ‘the amorous dog-chase might well have led you into Mr Period’s garden.’

‘It might have,’ Desirée remarked, ‘but in point of fact it didn’t. Bimbo was never out of my sight.’

‘If that is so,’ Alleyn said, ‘it leads us to an inescapable conclusion.’

He waited, and across the stillness of the room there floated small, inconsequent sounds: the whisper of Fox’s pencil and his rather heavy breathing, the faint rasp of Moppett’s fingernails on the arms of her chair and from somewhere within the house a scarcely perceptible mechanical throb.

‘There remains,’ Alleyn said, ‘just one person to whom opportunity, behaviour and motive all point, inescapably. This person presents certain characteristics: a knowledge of Mr Cartell’s movements, the assurance that at one o’clock the Baynesholme guests would have long ago left the scene, and access to Mr Leiss’s gloves. So much for opportunity. Behaviour. There are certain reactions. Everybody knows about Mr Period’s propensity for writing letters of condolence; he’s famous for them. Now, suppose one of you gets a Period letter, couched in rather ambiguous terms but commiserating with you on the loss of somebody whom you saw fighting-fit the previous evening. What would you think? Either that he was dotty or that he had sent you the wrong letter. You might get an initial shock, but a few moments thought would reassure you. You would not, having gone to find out what it was all about and encountered a bewildered Mr Period, turn deadly white and almost faint. But if you had murdered the supposed subject of the letter, how would you react? Suppose you had awakened in the morning with the remembrance of your deed festering in your mind and then been presented with this letter. Suppose, finally, that when you were being interviewed by the police, a second letter arrived, couched in exactly the same phrases. Wouldn’t that seem like a nightmare? Wouldn’t it seem as if Mr Period knew what you’d done and was torturing you with his knowledge? What would you do then?’