Tommy Johns was at once very still. He leant forward, his arms flexed and hanging free of his body, his chin lowered. ‘I’d got no call to do it,’ he said. ‘Why would I want to do it? She treated me fair enough according to her ideas. I’ve got no motive.’

‘I imagine,’ Alleyn said, ‘it’s a fairly open secret on the place that the work Captain Grace and Mr Losse have been doing together is of military importance. That it is, in fact, an experimental war job and, as such, has been carried out in secrecy. You also know that Mrs Rubrick was particularly interested in anti-espionage precautions.’

‘I don’t know anything about that,’ Tommy Johns began, but Alleyn interrupted him. ‘You don’t see a windmill put up at a considerable expense to provide an electric supply for one room only, and that a closely-guarded workroom, without wondering what it’s in aid of. Mrs Rubrick herself seems to have adopted a somewhat obvious attitude of precaution and mystery. The police investigation was along unmistakable lines. You can’t have failed to see that they were making strenuous efforts to link up murder with possible espionage. To put it bluntly, your name appears in the list of persons who might turn out to be agents in the pay of an enemy power, and therefore suspects in the murder of Mrs Rubrick. Of course, there’s a far more obvious motive: anger at Mrs Rubrick’s attitude towards your son in the matter of the stolen whisky, and fear of any further steps she might take.’

Tommy Johns uttered an extremely raw expletive.

‘I only mention it,’ said Alleyn, ‘to remind you that Cliff’s “grilling” as you call it, was in no way peculiar to him. Your turn may come, but not tonight. I’ve got to start work at five, and I must get some sleep. You pipe down like a sensible chap. If you and your boy had no hand in these assaults, you’ve nothing to worry about.’

‘I’m not so sure,’ he said, blinking. ‘The wife’s had about as much as she can take,’ he added indistinctly, and looked at Alleyn from under his jutting brows. ‘Oh, well,’ he said.

‘Murder takes it out of all hands,’ Alleyn murmured, piloting him to the door. Johns halted in front of Markins. ‘What’s he doing in here?’ he demanded.

‘I’m OK, Tommy,’ said Markins. ‘Don’t start in on me now.’

‘I haven’t forgot it was you that put the boy away with her in the first instance,’ said Johns. ‘The boy asked us not to let it make an unpleasantness, so we didn’t. But I haven’t forgot. You’re the fancy witness in this outfit, aren’t you? What’s he pay you for it?’