"Quick!" he urged his brother.
Joe leaped and scrambled into the opening.
At the same instant the foremost wolf crouched for a spring. There was not a second to lose. Frank leveled the revolver and fired.
His aim was true. Halfway in the air the animal gave a convulsive twist of its body and crashed on to the rocks. It writhed in its death agony, snarling ferociously and snapping at everything within reach, until it finally lay still.
The respite was just what the boys needed. The other wolves slunk back, discouraged by the loss of their leader. Frank knew, however, that it would be but for a moment. He backed into the passage with Joe.
The tunnel was narrow, but high enough to permit them to move about without crouching. They were unable to light their way, as Frank needed the flashlight turned before him in order to frighten back the wolves. For a moment the animals seemed to hesitate, as though fearing a trap and then the foremost wolf cautiously entered the tunnel in pursuit of its prey.
The boys backed slowly down the tunnel, which descended on a slope. They did not know where it led, they could not see, but they knew they must keep backing away from the wolves.
"We're up against it if this is a blind alley," declared Joe, in a low voice.
"We're up against it if we stop and try to fight it out."
Step by step they moved backward, and step by step the foremost wolf pursued them.