As he locked up the letter with the receipt, the association of ideas reminded him of Obenreizer.  A guess at the identity of the suspected man looked more possible now.  Obenreizer might know.

The thought had barely passed through his mind, when the door opened, and Obenreizer entered the room.

“They told me at Soho Square you were expected back last night,” said Vendale, greeting him.  “Have you done well in the country?  Are you better?”

A thousand thanks.  Obenreizer had done admirably well; Obenreizer was infinitely better.  And now, what news?  Any letter from Neuchatel?

“A very strange letter,” answered Vendale.  “The matter has taken a new turn, and the letter insists—­without excepting anybody—­on my keeping our next proceedings a profound secret.”

“Without excepting anybody?” repeated Obenreizer.  As he said the words, he walked away again, thoughtfully, to the window at the other end of the room, looked out for a moment, and suddenly came back to Vendale.  “Surely they must have forgotten?” he resumed, “or they would have excepted me?”

“It is Monsieur Rolland who writes,” said Vendale.  “And, as you say, he must certainly have forgotten.  That view of the matter quite escaped me.  I was just wishing I had you to consult, when you came into the room.  And here I am tried by a formal prohibition, which cannot possibly have been intended to include you.  How very annoying!”

Obenreizer’s filmy eyes fixed on Vendale attentively.

“Perhaps it is more than annoying!” he said.  “I came this morning not only to hear the news, but to offer myself as messenger, negotiator—­what you will.  Would you believe it?  I have letters which oblige me to go to Switzerland immediately.  Messages, documents, anything—­I could have taken them all to Defresnier and Rolland for you.”

“You are the very man I wanted,” returned Vendale.  “I had decided, most unwillingly, on going to Neuchatel myself, not five minutes since, because I could find no one here capable of taking my place.  Let me look at the letter again.”

He opened the strong room to get at the letter.  Obenreizer, after first glancing round him to make sure that they were alone, followed a step or two and waited, measuring Vendale with his eye.  Vendale was the tallest man, and unmistakably the strongest man also of the two.  Obenreizer turned away, and warmed himself at the fire.

Meanwhile, Vendale read the last paragraph in the letter for the third time.  There was the plain warning—­there was the closing sentence, which insisted on a literal interpretation of it.  The hand, which was leading Vendale in the dark, led him on that condition only.  A large sum was at stake:  a terrible suspicion remained to be verified.  If he acted on his own responsibility, and if anything happened to defeat the object in view, who would be blamed?  As a man of business, Vendale had but one course to follow.  He locked the letter up again.