‘Well, I know that,’ Coombe said quickly. He had just been warned against the axiomatic sin of forming a theory too soon. ‘Here are these chaps now,’ he said.

Two policemen were walking over the causeway.

Alleyn said: ‘Look, Coombe. I think our next step had better be the boy. Dr Maine saw him and so did Miss Pride. Could you set your men to patrol the path and then join me at Trehern’s cottage?’

‘There may be a mob of visitors there. It’s a big attraction.’

‘Hell! Hold on. Wait a bit, would you?’

Alleyn had seen Jenny Williams coming out of the old pub. She wore an orange-coloured bathing dress and a short white coat and looked as if she had had twice her fair share of sunshine.

He joined her. ‘It’s all fixed with Miss Emily,’ she said, ‘I’m a lady’s companion as from tomorrow morning. In the meantime, Patrick and I are thinking of a bathe.’

‘I don’t know what we’d have done without you. And loath as I am to put anything between you and the English Channel, I have got another favour to ask.’

‘Now, what is all this?’

‘You know young Trehern, don’t you? You taught him? Do you get on well with him?’

‘He didn’t remember me at first. I think he does now. They’ve done their best to turn him into a horror but – yes – I can’t help having a – I suppose it’s a sort of compassion,’ said Jenny.

‘I expect it is,’ Alleyn agreed. He told her he was going to see Wally and that he’d heard she understood the boy and got more response from him than most people. Would she come down to the cottage and help with the interview?

Jenny looked very straight at him and said: ‘Not if it means you want me to get Wally to say something that may harm him.’

Alleyn said: ‘I don’t know what he will say. I don’t in the least know whether he is in any way involved in Miss Cost’s death. Suppose he was. Suppose he killed her, believing her to be Miss Emily. Would you want him to be left alone to attack the next old lady who happened to annoy him? Think.’