The rocks above were much larger than they had seemed from the sub.  Twice, as he climbed over them, Dave’s foot slipped and each time his heart was in his mouth.  One stumbling misstep and all might be over for him.  But he had the clear, cool head of a clean boy who had lived right, and an appreciation of the joy of living, which would take him far and keep him safe through many an adventure.  So, safely, they reached the top of the cliff.

The Doctor motioned Dave to come back with him to a box-like edge of rock, which would give them a view of what lay some three hundred feet below.  All was still.  The moon, a great yellow ball, floated in the sky above and in the sea beneath.  A lone sea-gull, awakened by the supporting party, sailed screaming away.  Not a move, not a sound was to be detected below.  Yet there, in a rocky cavern, were a number of world-criminals, and behind some crag were three jackies and their commander.  Soon all this would be changed.  Fighting, perhaps death, would end the quiet of that Arctic scene.  Dave’s hand trembled with excitement as he arranged the two sacks beside the Doctor.  Even the Doctor’s hand shook as he opened one sack and drew forth a number of small iron objects, the size and shape of a bicycle handle-bar grip.  His face grew stern.

“Understand Mill’s grenades?” he asked.

“Yes.”

“All right.  When I say ‘Go’ drop ten of these as fast as you can release the pins.  Drop ’em on their shack.”

Dave’s heart thumped violently.  He had thrown Mill’s grenades at manikin “enemies,” but never had he hurled them where human flesh was the target.  Slowly, mechanically, he arranged the ten grenades in a row.

“Go!” The word sang in his ears.

Ten seconds later from below came two sharp reports—­his grenade and the Doctor’s.  They were off together.  Crash followed crash in quick succession until the row was finished.  Silence followed for a single second.  Then came the cries and curses of men, as they staggered from their half-demolished shelter and began to scatter.  Dave’s heart thumped.  There were fifteen, at least.

“Now!” exclaimed the Doctor, and lifting one of the large spheres he dropped it over the ledge’s edge.  Just as that instance Dave saw one of the rascals raise his rifle and fire.  Immediately there came a cry of distress.  Dave thought he recognized the voice and a lump rose in his throat.

But now there came a dull muffled explosion—­the strange bomb.  Instantly the men below began acting like madmen.  Throwing away their rifles, they staggered about, tearing at their eyes, their throats, their clothing, and uttering wild cries of distress.  At the same time three automatic pistols cracked, and Dave knew the doctor had given his signal.

To his surprise, he saw the three jackies emerge from hiding wearing gas masks.  Quickly they overpowered the wild men, tied them and carried them around a point of land.  As they did this the Doctor and his band kept guard above, rifles ready for any man who might, by some chance, recover sufficiently from the gas to shoot.  But none did.