Carlo and talking to him face to face.

But with his keen intuitive sense, Lars Larssen felt that the
explanation was in some way connected with this mysterious John Rivière.
It was imperative to get in touch with the man.

Where was Rivière? Was there nobody who could throw light on his
whereabouts? His jaw tightened as he began to chew on the problem. Paris
is too big a city in which to hunt for a mere name.

After thanking the manager, Larssen withdrew from the room. Passing
through the outer office, he was addressed by the other of the two
clerks, a young Frenchman.

"Monsieur," said he in French, "here is a point which perhaps will be of
service. I am at the window when Monsieur Rivière arrives _en
taxi-auto_. On the _impériale_ I see a portmanteau. Doubtless Monsieur
Rivière journeys away from Paris."

"Did you note the number of the cab?"

The young Frenchman made a gesture of sympathetic negation. There had
been no reason to look at the number, even if he could have read it from
a window on the second story.

"Thanks," said Larssen, but the information seemed at first sight
valueless. A man takes an unknown cab from an unknown house in an
unknown suburb to an unknown terminus, when he buys a ticket for an
unknown destination. Sheer waste of energy to hunt for a needle in that
haystack!