“Well?” said Nigel.

“Unless the person who made them was sitting astride the bannister and facing the hall. Someone who had, for instance, slid down the bannister and fetched up leaning heavily on the knob. A person with a longish reach could, from that position, have just got hold of the knife as it hung on the leather strip against the wall. Such a person would have been considerably higher than the stooping victim. We re-examined the entire length of the rail. At the top we found similar prints consistent with my idea that their author had slid down the bannister face first. I asked Miss Angela if any of you had been indulging in this mild sport and she told me no— not this week-end. I also ascertained that Doctor Tokareff and Mrs. Wilde were no good at it. This was not particularly interesting as the prints were not those of any of these persons.”

“Then whose—?”

“We next turned our attention to the outer border of the bottom of the bannister, the wooden base into which the uprights are set. Here we found a print, solitary and unmistakable since Ethel, Mary and Co. don’t fancy poking a duster through the rails. It was incisive at the top and blurred further down.”

“But how could anyone get their hand through the rails, and why should they?”

“It was not the print of a hand, but of a naked foot, a foot that had just brushed the wood as its owner slid down the bannister. And with that discovery. I had to reconstruct my ideas about the time factor. It gave me about ten seconds more room to think about in. A vivid little scene had begun to take shape. Picture it, Bathgate. The hall is dimly lit. Mary has turned off most of the lights, having a mania for this manœuvre. She has gone out and Rankin is bending over the cocktail tray, clearly lit by the wall lamp above it. The stairs are practically in darkness. Rankin is probably shaking up the last of the cocktail, preparatory to pouring it out. At the top of the stairs appears a dim, half-clad figure. It may be wearing a dressing-gown or perhaps it is only clad in underclothes. A glove is on its right hand. There is a faint swishing noise, drowned by the gurgle of the cocktail shaker. The figure is now astride the bottom of the bannister. It makes two swift gestures and Rankin pitches forward, striking the gong with his head. The figure on the bannister leans far out and reaches towards the switch. Then complete darkness.”

Alleyn stopped speaking.

“Well,” ventured Nigel with shaky facetiousness. “Am I now supposed to know the answer?”

Alleyn looked at him with a curious air of compassion.

“Not even yet?” he said.

“Whose were the prints?”

“That I am not going to tell you. Oh, believe me, Bathgate, not out of any desire to figure as the mysterious omnipotent detective. That would be impossibly vulgar. No. I am not telling you because there is still that bit of my brain that cannot quite accept the Q.E.D. of the theorem. There is only one tangible bit of evidence in this whole case. That is the button of the glove worn by the murderer. The glove was burnt, but the fastening, a press-button, was recovered. That miserable little button fastens the whole structure of my case. It is not enough. So I have decided to make an extraordinary experiment, Bathgate. I am going to ask the group of suspected persons to look on while we go through a performance of the murder. One of the guests must slide down the bannister and in dumb-show re-enact that terrible little scene. I want you, with the ‘very comment of your soul,’ if that was the phrase, to observe the others. Yes, it’s Hamlet’s old stunt over again and if it comes off I hope I shan’t make the muck he did of the result. You have made some friends here, haven’t you?”

“Yes,” answered Nigel, surprised

“Then I am afraid the result is going to come as a shock to you. For that reason I have told you this much. I have enjoyed your companionship, Bathgate,” ended the Chief Inspector with one of those curious twists of formality that Nigel had grown accustomed to. “Perhaps we may have a final talk together — afterwards.”

“I shall insist on it,” Nigel assured him.

“Well! Do one last job of work for me. Will you play the murderer’s part in the play within the play and help me to trick this shadowy figure into betraying itself?”

“I must say—” said Nigel coldly.

“Ah! you don’t care to do it. It is detestable to you. I hate illogical sentimentality. It is so conceited.”

There was a note of bitterness in Alleyn’s voice that Nigel had not heard before.

“You don’t understand—” he began.

“I think I do. For you it’s all over. Rankin was your cousin; you have had a shock. You have also, you must confess, enjoyed the part you have played up to date in helping to round up a bunch of mad Russians. But now, when a criminal who is prepared — even schemes — to let an innocent person hang, turns out to be someone you know, you become all fastidiousness and leave the dirt to the policeman. Quite understandable. In a couple of years you will be dining out on this murder. Pity you can’t write it up.”

“You’re unfair,” said Nigel angrily.

“Am I? Well, don’t let’s quarrel. Perhaps you wouldn’t mind asking Bunce, who is out on the drive, to report to me. I am afraid that it is part of my schedule that you should witness, with the others, this final scene. Your train goes in half an hour.”

Nigel walked to the door. “I’ll tell Bunce,” he volunteered.

“Thank you,” said Alleyn wearily.

“And,” continued Nigel rather indistinctly, “I still think you are unfair, Alleyn, but if you like, if you’ll allow me to — I’ll do whatever you suggest to help.”

Alleyn’s singularly charming smile lightened his eyes for a moment.

“All right,” he said. “Sorry! I’m a bundle of nerves at the moment, and I do so hate murders. Perhaps someone else will do, after all. Come back with the bluebottle and I’ll explain.”

Nigel found Bunce, P.C., staring disconsolately at a dead chrysanthemum in a border by the side lawn.

“Chief Inspector-Detective Alleyn wants you in the study,” said Nigel, enjoying the rhymic sequence of the titles and name.

“Oh!” said Bunce, rousing himself. “Thank you, sir, I’ll come along. It’ll be a bit of a change after these urbashus borders. I’m not a great nature-lover myself.”

“No?”

“No. Altogether too ’ap’azard to my way of thinking. Sloppy. That’s Nature. Well, I’ll be shifting.”

“I’m coming too,” said Nigel, and they returned in silence to the study.

Alleyn was standing by the fireplace examining a revolver. He slipped it into his pocket.

“Bunce,” he said crisply, “have a man outside the front door in ten minutes’ time, another in the drawing-room and a third here. The members of the household will then be assembled in the hall. Keep your wits about you and your ears well open. When you hear me say, ‘Now, let us begin,’ come very quietly into the hall and keep the person, of whom I have already informed you, under observation. I expect no trouble, but — well, the quieter the better. The arrest will probably take place immediately. By the way, I shall want you to impersonate the victim as you did during the first reconstruction.”

Bunce’s eye lightened.

“Very good, sir. ’Ead first into the gong as usual, I presoom?”

“Yes, Bunce. You may retain your helmet if you like.”

“ ’Ardly artistic would it be, sir? I shan’t notice the blow in my excitement.”

“As you please. Very well then, off you go. Place your men now, will you, and don’t discuss anything. That clear?”

“Abundantly, sir,” ejaculated Bunce. He turned about smartly and left the room by the French window.

“Now, Bathgate,” said Alleyn, “I shall make certain of everybody being in the hall in half an hour. The cars will be outside to take you all to the station. Miss Angela has just returned so we shall be complete — with the exception of the Russians of course. By the way, Bathgate, can you slide down bannisters face first?”