‘How do you reckon he brought it off? With what?’

‘Back to the jurists’ maxim,’ said Alleyn with a slight smile: ‘Quis, quid, ubi, quibus auxiliis, cur, quomodo, quando?’

‘I never can remember it that way,’ said Fox, ‘knowing no Latin. But I’ve got old Gross’s rhyme all right:

‘What was the crime, who did it, when was it done, and where?

How done, and with what motive, who in the deed did share?’

‘Yes,’ said Alleyn. ‘We’ve got quid, quomodo and ubi, but we’re not so sure of quibus auxiliis. Dr Curtis says the abrasion on the temple is two and a half inches long and one-twelfth of an inch across. The blow, he thinks, was not necessarily very heavy, but sharp and extremely accurate. What sort of implement does that suggest to you, Fox?’

‘I’ve been thinking that—’

The desk telephone rang. Alleyn answered it.

‘Hullo?’

‘Mr Alleyn? The Yard here. Sir Daniel Davidson has rung up and says he may have something to tell you. He’ll be in all day.’

‘Where is he?’

‘In his rooms, number fifty St. Luke’s Chambers, Harley Street.’

‘Say I’ll call at two o’clock. Thank him.’ Alleyn put the receiver down.

‘Davidson,’ he said, ‘thinks he may have something to relate. I bet he had a heart-to-heart talk with himself before he decided to ring up.’

‘Why?’ asked Fox. ‘Do you mean he feels shaky?’

‘I mean he’s a fashionable doctor and they don’t care for the kind of publicity you get from criminal investigations. If he’s a clever fellow, and I imagine he must be to have got where he is, he’s realized he was one of the last people to see Lord Robert. He’s decided to come to us before we go to him. According to your notes, Fox, Sir Daniel was the first of the last three people to leave before Lord Robert. The other two were a tight young gentleman and a female secretary. Sir Daniel would have seen Lord Robert was alone and about to leave. He could have waited outside in the mist and asked for a lift in the taxi as easily as anybody. I wonder if he realizes that.’

‘No motive,’ said Fox.

‘None, I should imagine. I mustn’t get fantastic, must I? Damn young Potter, why doesn’t he come?’

‘Have you finished here, sir?’

‘Yes. I got here at five o’clock this morning, broke the news to Lady Mildred, and settled down to Lord Robert’s dressing-room, bedroom and this study. There’s nothing at all to be found except his notes and the will. From seven until ten I looked in their garden, the neighbouring gardens and up and down the Embankment for a cloak and a soft hat. With no success. I’ve got a squad of men at it now.’

‘He may not have got rid of them.’