After a little while they had coffee.

‘A little logical thinking would be in order, I fancy,’ said Wexford. ‘You said this morning that we were not so much seeking to prove murder as attempted murder. Axel Kingman could have pushed her off that balcony, but no one saw her fall and no one heard him or anybody else go up to that flat during the afternoon. If, however, an attempt to murder her was made two weeks before, the presumption that she was eventually murdered is enormously strengthened.’

Burden said impatiently, ‘We’ve been through all that. We know that.’

‘Wait a minute. The attempt failed. Now just how seriously ill was she? According to Kingman and Hood, she had severe stomach pains and she vomited. By midnight she was peacefully sleeping and by the following day she was all right.’

‘I don’t see where all this is getting us.’

‘To a point which is very important and which may be the crux of the whole case. You say that Axel Kingman attempted to murder her. In order to do so he must have made very elaborate plans – the arranging of the meal, the inviting of the two witnesses, the ensuring that his wife tasted the stew earlier in the same day, and the preparation for some very nifty sleight of hand at the time the meal was served. Isn’t it odd that the actual method used should so signally have failed? That Hannah’s life never seems to have been in danger? And what if the method had succeeded? At post-mortem some noxious agent would have been found in her body or the effects of such. How could he have hoped to get away with that since, as we know, neither of his witnesses actually watched him serve Hannah and one of them was even out of the room?

‘So what I am postulating is that no one attempted to murder her, but someone attempted to make her ill so that, taken in conjunction with the sinister reputation of non-mushroom fungi and Hood’s admitted suspicion of them, taken in conjunction with the known unhappiness of the marriage, it would look as if there had been a murder attempt.’

Burden stared at him. ‘Kingman would never have done that. He would either have wanted his attempt to succeed or not to have looked like an attempt at all.’

‘Exactly. And where does that get us?’

Instead of answering him, Burden said on a note of triumph, his humiliation still rankling, ‘You’re wrong about one thing. She was seriously ill, she didn’t just have nausea and vomiting. Kingman and Hood may not have mentioned it, but Corinne Last said she had double vision and black spots before her eyes and . . .’ His voice faltered. ‘My God, you mean . . .?’

Wexford nodded. ‘Corinne Last only of the three says she had those symptoms. Only Corinne Last is in a position to say, because she lived with him, if Kingman was in the habit of rinsing plates as soon as he removed them from the table. What does she say? That she doesn’t know. Isn’t that rather odd? Isn’t it rather odd too that she chose that precise moment to leave the table and go out into the hall for her handbag?