the cab. When he picked himself up he found he was on Hampstead Heath; so he took a bus home, and there he lies now on the sofa, while I came straight round to tell you what had happened.’

‘Most interesting,’ said Holmes. ‘Did he observe the appearance of these men—did he hear them talk?’

‘No; he is clean dazed. He just knows that he was lifted up as if by magic and dropped as if by magic. Two at least were in it, and maybe three.’

‘And you connect this attack with your lodger?’

‘Well, we’ve lived there fifteen years and no such happenings ever came before. I’ve had enough of him. Money’s not everything. I’ll have him out of my house before the day is done.’

‘Wait a bit, Mrs Warren. Do nothing rash. I begin to think that this affair may be very much more important than appeared at first sight. It is clear now that some danger is threatening your lodger. It is equally clear that his enemies, lying in wait for him near your door, mistook your husband for him in the foggy morning light. On discovering their mistake they released him. What they would have done had it not been a mistake, we can only conjecture.’

‘Well, what am I to do, Mr Holmes?’

‘I have a great fancy to see this lodger of yours, Mrs Warren.’

‘I don’t see how that is to be managed, unless you break in the door. I always hear him unlock it as I go down the stair after I leave the tray.’

‘He has to take the tray in. Surely we could conceal ourselves and see him do it.’

The landlady thought for a moment.

‘Well, sir, there’s the box-room opposite. I could arrange a looking-glass, maybe, and if you were behind the door—’

‘Excellent!’ said Holmes. ‘When does he lunch?’

‘About one, sir.’

‘Then Dr Watson and I will come round in time. For the present, Mrs Warren, good-bye.’

At half-past twelve we found ourselves upon the steps of Mrs Warren’s house—a high, thin, yellow- brick edifice in Great Orme Street, a narrow thoroughfare at the north-east side of the British Museum. Standing as it does near the corner of the street, it commands a view down Howe Street, with its more pretentious houses. Holmes pointed with a chuckle to one of these, a row of residential flats, which projected so that they could not fail to catch the eye.

‘See, Watson!’ said he. ‘ “High red house with stone facings.” There is the signal station all right. We know the place, and we know the code; so surely our task should be simple. There’s a “To Let” card in that window. It is evidently an empty flat to which the confederate has access. Well, Mrs Warren, what now?’

‘I have it all ready for you. If you will both come up and leave your boots below on the landing, I’ll put you there now.’

It was an excellent hiding-place which she had arranged. The mirror was so placed that, seated in the dark, we could very plainly see the door opposite. We had hardly settled down in it, and Mrs Warren left us, when a distant tinkle announced that our mysterious neighbour had rung. Presently the landlady