Bur-r-r-r! The telephone bell struck an odd, imperative note at that moment, and Von Dussel spoke sharply.
"You hear that, you hound?" he thundered. "You Dashwoods, you! How long have you been here?"
They knew it was only a ruse to make them betray themselves, prompted by their enemy's keen anxiety to answer the summons, and they stood behind the boiler perfectly still.
Bur-r-r-r!
"So you will not speak," snarled Von Dussel. "Very well, I am going to answer that message. I shall have a Browning pistol in one hand and the receiver in the other. You had better look out; you will never leave this room alive, either of you."
Dennis, groping silently in front of him along the brick base in which the boiler was fixed, had found a heavy screw wrench, and, repeating his former manœuvre, hurled it this time to the opposite end of the engine-room.
It dropped with a loud clang; but Von Dussel was on his guard, and before he fired he switched his light on for an instant, and Dennis pulled the trigger of the rifle.
It was only for a second's space that Dennis saw the man with his hand raised, and he could not repress a fierce shout of joy as a Mauser bullet dashed the Browning pistol from Von Dussel's hand.
"Perhaps we English are not such fools, after all!" he laughed. But when the spy's voice answered him, it was from the opposite side of the room.
"That remains to be seen," was his reply. "I tell you, you will not leave this place alive. The brewery is mined, and I am going to fire the charge. Good night. I will send Madame Dashwood a field post card to-morrow!"