‘Come in!’ called Trent.

Mr. Cupples entered his sitting-room at the hotel. It was the early evening of the day on which the coroner’s jury, without leaving the box, had pronounced the expected denunciation of a person or persons unknown. Trent, with a hasty glance upward, continued his intent study of what lay in a photographic dish of enamelled metal, which he moved slowly about in the light of the window. He looked very pale, and his movements were nervous.

‘Sit on the sofa,’ he advised. ‘The chairs are a job lot bought at the sale after the suppression of the Holy Inquisition in Spain. This is a pretty good negative,’ he went on, holding it up to the light with his head at the angle of discriminating judgement. ‘Washed enough now, I think. Let us leave it to dry, and get rid of all this mess.’

Mr. Cupples, as the other busily cleared the table of a confusion of basins, dishes, racks, boxes, and bottles, picked up first one and then another of the objects and studied them with innocent curiosity.

‘That is called hypo-eliminator,’ said Trent, as Mr. Cupples uncorked and smelt at one of the bottles. ‘Very useful when you’re in a hurry with a negative. I shouldn’t drink it, though, all the same. It eliminates sodium hypophosphite, but I shouldn’t wonder if it would eliminate human beings too.’ He found a place for the last of the litter on the crowded mantel-shelf, and came to sit before Mr. Cupples on the table. ‘The great thing about a hotel sitting-room is that its beauty does not distract the mind from work. It is no place for the mayfly pleasures of a mind at ease. Have you ever been in this room before, Cupples? I have, hundreds of times. It has pursued me all over England for years. I should feel lost without it if, in some fantastic, far-off hotel, they were to give me some other sitting-room. Look at this table-cover; there is the ink I spilt on it when I had this room in Halifax. I burnt that hole in the carpet when I had it in Ipswich. But I see they have mended the glass over the picture of “Silent Sympathy”, which I threw a boot at in Banbury. I do all my best work here. This afternoon, for instance, since the inquest, I have finished several excellent negatives. There is a very good dark room downstairs.’

‘The inquest—that reminds me,’ said Mr. Cupples, who knew that this sort of talk in Trent meant the excitement of action, and was wondering what he could be about. ‘I came in to thank you, my dear fellow, for looking after Mabel this morning. I had no idea she was going to feel ill after leaving the box; she seemed quite unmoved, and, really, she is a woman of such extraordinary self-command, I thought I could leave her to her own devices and hear out the evidence, which I thought it important I should do. It was a very fortunate thing she found a friend to assist her, and she is most grateful. She is quite herself again now.’

Trent, with his hands in his pockets and a slight frown on his brow, made no reply to this. ‘I tell you what,’ he said after a short pause, ‘I was just getting to the really interesting part of the job when you came in. Come; would you like to see a little bit of high-class police work? It’s the very same kind of work that old Murch ought to be doing at this moment. Perhaps he is; but I hope to glory he isn’t.’ He sprang off the table and disappeared into his bedroom. Presently he came out with a large drawing-board on which a number of heterogeneous objects was ranged.

‘First I must introduce you to these little things,’ he said, setting them out on the table. ‘Here is a big ivory paper-knife; here are two leaves cut out of a diary—my own diary; here is a bottle containing dentifrice; here is a little case of polished walnut. Some of these things have to be put back where they belong in somebody’s bedroom at White Gables before night. That’s the sort of man I am—nothing stops me. I borrowed them this very morning when every one was down at the inquest, and I dare say some people would think it rather an odd proceeding if they knew. Now there remains one object on the board. Can you tell me, without touching it, what it is?’

‘Certainly I can,’ said Mr. Cupples, peering at it with great interest. ‘It is an ordinary glass bowl. It looks like a finger-bowl. I see nothing odd about it,’ he added after some moments of close scrutiny.

‘I can’t see much myself,’ replied Trent, ‘and that is exactly where the fun comes in. Now take this little fat bottle, Cupples, and pull out the cork. Do you recognize that powder inside it? You have swallowed pounds of it in your time, I expect. They give it to babies. Grey powder is its ordinary name—mercury and chalk. It is great stuff. Now, while I hold the basin sideways over this sheet of paper, I want you to pour a little powder out of the bottle over this part of the bowl—just here.... Perfect! Sir Edward Henry himself could not have handled the powder better. You have done this before, Cupples, I can see. You are an old hand.’

‘I really am not,’ said Mr. Cupples seriously, as Trent returned the fallen powder to the bottle. ‘I assure you it is all a complete mystery to me. What did I do then?’

‘I brush the powdered part of the bowl lightly with this camel-hair brush. Now look at it again. You saw nothing odd about it before. Do you see anything now?’

Mr. Cupples peered again. ‘How curious!’ he said. ‘Yes, there are two large grey finger-marks on the bowl. They were not there before.’

‘I am Hawkshaw the detective,’ observed Trent. ‘Would it interest you to hear a short lecture on the subject of glass finger-bowls? When you take one up with your hand you leave traces upon it, usually practically invisible, which may remain for days or months. You leave the marks of your fingers. The human hand, even when quite clean, is never quite dry, and sometimes—in moments of great anxiety, for instance, Cupples—it is very moist. It leaves a mark on any cold smooth surface it may touch. That bowl was moved by somebody with a rather moist hand quite lately.’ He sprinkled the powder again. ‘Here on the other side, you see, is the thumb-mark—very good impressions all of them.’ He spoke without raising his voice, but Mr. Cupples could perceive that he was ablaze with excitement as he stared at the faint grey marks. ‘This one should be the index finger. I need not tell a man of your knowledge of the world that the pattern of it is a single-spiral whorl, with deltas symmetrically disposed. This, the print of the second finger, is a simple loop, with a staple core and fifteen counts. I know there are fifteen, because I have just the same two prints on this negative, which I have examined in detail. Look!’—he held one of the negatives up to the light of the declining sun and demonstrated with a pencil point. ‘You can see they’re the same. You see the bifurcation of that ridge. There it is in the other. You see that little scar near the centre. There it is in the other. There are a score of ridge-characteristics on which an expert would swear in the witness-box that the marks on that bowl and the marks I have photographed on this negative were made by the same hand.’

‘And where did you photograph them? What does it all mean?’ asked Mr Cupples, wide-eyed.

‘I found them on the inside of the left-hand leaf of the front window in Mrs. Manderson’s bedroom. As I could not bring the window with me, I photographed them, sticking a bit of black paper on the other side of the glass for the purpose. The bowl comes from Manderson’s room. It is the bowl in which his false teeth were placed at night. I could bring that away, so I did.’

‘But those cannot be Mabel’s finger-marks.’

‘I should think not!’ said Trent with decision. ‘They are twice the size of any print Mrs. Manderson could make.’

‘Then they must be her husband’s.’

‘Perhaps they are. Now shall we see if we can match them once more? I believe we can.’ Whistling faintly, and very white in the face, Trent opened another small squat bottle containing a dense black powder. ‘Lamp-black,’ he explained. ‘Hold a bit of paper in your hand for a second or two, and this little chap will show you the pattern of your fingers.’ He carefully took up with a pair of tweezers one of the leaves cut from his diary, and held it out for the other to examine. No marks appeared on the leaf. He tilted some of the powder out upon one surface of the paper, then, turning it over, upon the other; then shook the leaf gently to rid it of the loose powder. He held it out to Mr. Cupples in silence. On one side of the paper appeared unmistakably, clearly printed in black, the same two finger-prints that he had already seen on the bowl and on the photographic plate. He took up the bowl and compared them. Trent turned the paper over, and on the other side was a bold black replica of the thumb-mark that was printed in grey on the glass in his hand.

‘Same man, you see,’ Trent said with a short laugh. ‘I felt that it must be so, and now I know.’ He walked to the window and looked out. ‘Now I know,’ he repeated in a low voice, as if to himself. His tone was bitter. Mr. Cupples, understanding nothing, stared at his motionless back for a few moments.

‘I am still completely in the dark,’ he ventured presently. ‘I have often heard of this fingerprint business, and wondered how the police went to work about it. It is of extraordinary interest to me, but upon my life I cannot see how in this case Manderson’s fingerprints are going—’

‘I am very sorry, Cupples,’ Trent broke in upon his meditative speech with a swift return to the table. ‘When I began this investigation I meant to take you with me every step of the way. You mustn’t think I have any doubts about your discretion if I say now that I must hold my tongue about the whole thing, at least for a time. I will tell you this: I have come upon a fact that looks too much like having very painful consequences if it is discovered by any one else.’ He looked at the other with a hard and darkened face, and struck the table with his hand. ‘It is terrible for me here and now. Up to this moment I was hoping against hope that I was wrong about the fact. I may still be wrong in the surmise that I base upon that fact. There is only one way of finding out that is open to me, and I must nerve myself to take it.’ He smiled suddenly at Mr. Cupples’s face of consternation. ‘All right—I’m not going to be tragic any more, and I’ll tell you all about it when I can. Look here, I’m not half through my game with the powder-bottles yet.’

He drew one of the defamed chairs to the table and sat down to test the broad ivory blade of the paper knife. Mr. Cupples, swallowing his amazement, bent forward in an attitude of deep interest and handed Trent the bottle of lamp-black.