“You see, colonel,” he said, “I was shut up in that small room there doing some writing, when I heard a pair of feet in this passage doing a dance that was as queer as the dance of death.  First came quick, funny little steps, like a man walking on tiptoe for a wager; then came slow, careless, creaking steps, as of a big man walking about with a cigar.  But they were both made by the same feet, I swear, and they came in rotation; first the run and then the walk, and then the run again.  I wondered at first idly and then wildly why a man should act these two parts at once.  One walk I knew; it was just like yours, colonel.  It was the walk of a well-fed gentleman waiting for something, who strolls about rather because he is physically alert than because he is mentally impatient.  I knew that I knew the other walk, too, but I could not remember what it was.  What wild creature had I met on my travels that tore along on tiptoe in that extraordinary style?  Then I heard a clink of plates somewhere; and the answer stood up as plain as St. Peter’s.  It was the walk of a waiter—­that walk with the body slanted forward, the eyes looking down, the ball of the toe spurning away the ground, the coat tails and napkin flying.  Then I thought for a minute and a half more.  And I believe I saw the manner of the crime, as clearly as if I were going to commit it.”

Colonel Pound looked at him keenly, but the speaker’s mild grey eyes were fixed upon the ceiling with almost empty wistfulness.

“A crime,” he said slowly, “is like any other work of art.  Don’t look surprised; crimes are by no means the only works of art that come from an infernal workshop.  But every work of art, divine or diabolic, has one indispensable mark—­I mean, that the centre of it is simple, however much the fulfilment may be complicated.  Thus, in Hamlet, let us say, the grotesqueness of the grave-digger, the flowers of the mad girl, the fantastic finery of Osric, the pallor of the ghost and the grin of the skull are all oddities in a sort of tangled wreath round one plain tragic figure of a man in black.  Well, this also,” he said, getting slowly down from his seat with a smile, “this also is the plain tragedy of a man in black.  Yes,” he went on, seeing the colonel look up in some wonder, “the whole of this tale turns on a black coat.  In this, as in Hamlet, there are the rococo excrescences—­yourselves, let us say.  There is the dead waiter, who was there when he could not be there.  There is the invisible hand that swept your table clear of silver and melted into air.  But every clever crime is founded ultimately on some one quite simple fact—­some fact that is not itself mysterious.  The mystification comes in covering it up, in leading men’s thoughts away from it.  This large and subtle and (in the ordinary course) most profitable crime, was built on the plain fact that a gentleman’s evening dress is the same as a waiter’s.  All the rest was acting, and thundering good acting, too.”