‘Are you thinking of some particular instance, Sir Henry?’ asked Mrs Bantry shrewdly.

‘As a matter of fact, Mrs Bantry, I am. A very curious case. A case where we believe murder to have been committed, but with no possible chance of ever proving it.’

‘Poison, I suppose,’ breathed Jane. ‘Something untraceable.’

Dr Lloyd moved restlessly and Sir Henry shook his head.

‘No, dear lady. Not the secret arrow poison of the South American Indians! I wish it were something of that kind. We have to deal with something much more prosaic—so prosaic, in fact, that there is no hope of bringing the deed home to its perpetrator. An old gentleman who fell downstairs and broke his neck; one of those regrettable accidents which happen every day.’

‘But what happened really?’

‘Who can say?’ Sir Henry shrugged his shoulders. ‘A push from behind? A piece of cotton or string tied across the top of the stairs and carefully removed afterwards? That we shall never know.’

‘But you do think that it—well, wasn’t an accident? Now why?’ asked the doctor.

‘That’s rather a long story, but—well, yes, we’re pretty sure. As I said there’s no chance of being able to bring the deed home to anyone—the evidence would be too flimsy. But there’s the other aspect of the case—the one I was speaking about. You see, there were four people who might have done the trick. One’s guilty; but the other three are innocent. And unless the truth is found out, those three are going to remain under the terrible shadow of doubt.’

‘I think,’ said Mrs Bantry, ‘that you’d better tell us your long story.’

‘I needn’t make it so very long after all,’ said Sir Henry. ‘I can at any rate condense the beginning. That deals with a German secret society—the Schwartze Hand—something after the lines of the Camorra or what is most people’s idea of the Camorra. A scheme of blackmail and terrorization. The thing started quite suddenly after the War, and spread to an amazing extent. Numberless people were victimized by it. The authorities were not successful in coping with it, for its secrets were jealously guarded, and it was almost impossible to find anyone who could be induced to betray them.

‘Nothing much was ever known about it in England, but in Germany it was having a most paralysing effect. It was finally broken up and dispersed through the efforts of one man, a Dr Rosen, who had at one time been very prominent in Secret Service work. He became a member, penetrated its inmost circle, and was, as I say, instrumental in bringing about its downfall.

‘But he was, in consequence, a marked man, and it was deemed wise that he should leave Germany—at any rate for a time. He came to England, and we had letters about him from the police in Berlin. He came and had a personal interview with me. His point of view was both dispassionate and resigned. He had no doubts of what the future held for him.