“Come,” he said, “we must go at once.”

“To-night?” queried Tuppence, surprised.

“To-morrow may be too late,” said Sir James gravely.  “Besides, by going to-night we have the chance of capturing that great man and super-criminal—­Mr. Brown!”

There was dead silence, and Sir James continued: 

“You have been followed here—­not a doubt of it.  When we leave the house we shall be followed again, but not molested, for it is Mr. Brown’s plan that we are to lead him.  But the Soho house is under police supervision night and day.  There are several men watching it.  When we enter that house, Mr. Brown will not draw back—­he will risk all, on the chance of obtaining the spark to fire his mine.  And he fancies the risk not great—­since he will enter in the guise of a friend!”

Tuppence flushed, then opened her mouth impulsively.

“But there’s something you don’t know—­that we haven’t told you.”  Her eyes dwelt on Jane in perplexity.

“What is that?” asked the other sharply.  “No hesitations, Miss Tuppence.  We need to be sure of our going.”

But Tuppence, for once, seemed tongue-tied.

“It’s so difficult—­you see, if I’m wrong—­oh, it would be dreadful.”  She made a grimace at the unconscious Jane.  “Never forgive me,” she observed cryptically.

“You want me to help you out, eh?”

“Yes, please.  You know who Mr. Brown is, don’t you?”

“Yes,” said Sir James gravely.  “At last I do.”

“At last?” queried Tuppence doubtfully.  “Oh, but I thought——­” She paused.

“You thought correctly, Miss Tuppence.  I have been morally certain of his identity for some time—­ever since the night of Mrs. Vandemeyer’s mysterious death.”

“Ah!” breathed Tuppence.

“For there we are up against the logic of facts.  There are only two solutions.  Either the chloral was administered by her own hand, which theory I reject utterly, or else——­”

“Yes?”

“Or else it was administered in the brandy you gave her.  Only three people touched that brandy—­you, Miss Tuppence, I myself, and one other—­Mr. Julius Hersheimmer!”

Jane Finn stirred and sat up, regarding the speaker with wide astonished eyes.

“At first, the thing seemed utterly impossible.  Mr. Hersheimmer, as the son of a prominent millionaire, was a well-known figure in America.  It seemed utterly impossible that he and Mr. Brown could be one and the same.  But you cannot escape from the logic of facts.  Since the thing was so—­it must be accepted.  Remember Mrs. Vandemeyer’s sudden and inexplicable agitation.  Another proof, if proof was needed.

“I took an early opportunity of giving you a hint.  From some words of Mr. Hersheimmer’s at Manchester, I gathered that you had understood and acted on that hint.  Then I set to work to prove the impossible possible.  Mr. Beresford rang me up and told me, what I had already suspected, that the photograph of Miss Jane Finn had never really been out of Mr. Hersheimmer’s possession——­”