‘Tom Addison. He’s colour blind. You know that, don’t you?’

‘Oh yes, of course. We all know that. That’s why he’s got odd shoes on today. He never knew red from green.’

‘This boy is the same.’

‘But–but surely not. Anyway, there’s never been any sign of it in–in Roland.’

‘There might be, though, mightn’t there?’ said Mr Satterthwaite. ‘I’m right in thinking–Daltonism. That’s what they call it, don’t they?’

‘It was a name they used to call it by, yes.’

‘It’s not inherited by a female, but it passes through the female. Lily wasn’t colour blind, but Lily’s son might easily be colour blind.’

‘But my dear Satterthwaite, Timothy isn’t Lily’s son. Roly is Lily’s son. I know they’re rather alike. Same age, same coloured hair and things, but–well, perhaps you don’t remember.’

‘No,’ said Mr Satterthwaite, ‘I shouldn’t have remembered. But I know now. I can see the resemblance too. Roland’s Beryl’s son. They were both babies, weren’t they, when Simon re-married. It is very easy for a woman looking after two babies, especially if both of them were going to have red hair. Timothy’s Lily’s son and Roland is Beryl’s son. Beryl’s and Christopher Eden’s. There is no reason why he should be colour blind. I know it, I tell you. I know it!’

He saw Dr Horton’s eyes go from one to the other. Timothy, not catching what they said but standing holding the blue cup and looking puzzled.

‘I saw her buy it,’ said Mr Satterthwaite. ‘Listen to me, man. You must listen to me. You’ve known me for some years. You know that I don’t make mistakes if I say a thing positively.’

‘Quite true. I’ve never known you make a mistake.’

‘Take that cup away from him,’ said Mr Satterthwaite. ‘Take it back to your surgery or take it to an analytic chemist and find out what’s in it. I saw that woman buy that cup. She bought it in the village shop. She knew then that she was going to break a red cup, replace it by a blue and that Timothy would never know that the colours were different.’

‘I think you’re mad, Satterthwaite. But all the same I’m going to do what you say.’

He advanced on the table, stretched out a hand to the blue cup.

‘Do you mind letting me have a look at that?’ said Dr Horton.

‘Of course,’ said Timothy. He looked slightly surprised.

‘I think there’s a flaw in the china, here, you know. Rather interesting.’

Beryl came across the lawn. She came quickly and sharply.

‘What are you doing? What’s the matter? What is happening?’