The Russian had already entered the tunnel.

Fred, when he followed him, heard him running up the long passage that led up to the house.

Before he could reach the opening, however, he heard other steps coming toward him, and a moment later Boris was heaping reproaches on him.
"I thought they had caught you!" he cried.

"I saw them chasing someone, and it looked like you.

In fact, I was sure it was you at first sight." "It was," said Fred, grimly.