‘Yes,’ said Davidson, and again that professional note sounded in his voice. ‘Yes. It’s not easy to give you the sort of answer you want. A healthy man would go in about four minutes if the murderer completely stopped all access of air to the lungs. A man with a condition of the heart which I believe to have obtained in this instance would be most unlikely to live for four minutes. Life might become extinct within less than two. He might die almost immediately.’

‘Yes. Thank you, sir.’

Alleyn said: ‘Suppose the murderer had some slight knowledge of medicine and was aware of Lord Robert’s condition, would he be likely to realize how little time he needed?’

‘That is rather a difficult question to answer. His slight knowledge might not embrace asphyxia. I should say that any first-year student would probably realize that a diseased heart would give out very rapidly under these conditions. A nurse would know. Indeed, I should have thought most laymen would think it probable. The actual time to within two or three minutes might not be appreciated.’

‘Yes. Thank you.’

Alleyn got up.

‘I think that really is everything. We’ll get out a statement for you to sign, if you will. Believe me, we do realize that it has been very difficult for you to speak of your patients under these extremely disagreeable circumstances. We’ll word the beastly document as discreetly as may be.’

‘I’m sure you will. Mr Alleyn, I think I remember Lord Robert telling me he had a great friend at Scotland Yard. Are you this friend? I see you are. Please don’t think my question impertinent. I am sure that you have suffered, with all his friends, a great loss. You should not draw too much upon your nervous energy, you know, in investigating this case. It is quite useless for me to tell you this, but I am a physician and I do know something about nerves. You are subjecting yourself to a very severe discipline at the moment. Don’t overdo it.’

‘Just what I’d like to tell him, sir,’ said Fox unexpectedly.

Davidson turned on him a face cordial with appreciation. ‘I see we understand each other, Mr Fox.’

‘It’s very kind of you both,’ said Alleyn with a grin, ‘but I’m not altogether a hothouse flower. Good-bye, Sir Daniel. Thank you so much.’

They shook hands and Fox and Alleyn went out.

‘Where do we go now?’ asked Fox.

‘I think we’d better take a look at Marsdon House. Bailey ought to have finished by now. I’ll ring up from there and see if I can get an appointment with the Carrados family en masse. It’s going to be difficult, that. There seems to be no doubt that Lady Carrados is one of the blackmailing victims. Carrados himself is a difficult type, a frightful old snob he is, and as vain as a peacock. Police investigation will undoubtedly stimulate all his worst qualities. He’s the sort of man who’d go to any lengths to avoid the wrong kind of publicity. We’ll have to go warily if we don’t want him to make fools of us and a confounded nuisance of himself.’