The Hairy Ones by Basil Wells - Marooned on a world within a world, aided by a slim girl and an old warrior, Patrolman Sisko Rolf was fighting his greatest battle—to bring life to dying Mars.

"The outlaw ships are attacking!" Old Garmon Nash's harsh voice snapped like a thunderclap in the cramped rocket flyer's cabin. "Five or six of them. Cut the searchlights!"

Sisko Rolf's stocky body was a blur of motion as he cut the rocket jets, doused the twin searchlights, and switched over to the audio beams that served so well on the surface when blind flying was in order. But here in the cavern world, thirty-seventh in the linked series of vast caves that underlie the waterless wastes of Mars, the reflected waves of sound were of little value. Distances were far too cramped—disaster might loom but a few hundred feet away.

"Trapped us neatly," Rolf said through clenched teeth. "Tolled into their underground hideout by that water-runner we tried to capture. We can't escape, that's certain. They know these caverns better than.... We'll down some of them, though."

"Right!" That was old Garmon Nash, his fellow patrolman aboard the Planet Patrol ship as he swung the deadly slimness of his rocket blast's barrel around to center on the fiery jets that betrayed the approaching outlaw flyers.

Three times he fired the gun, the rocket projectiles blasting off with their invisible preliminary jets of gas, and three times an enemy craft flared up into an intolerable torch of flame before they realized the patrol ship had fired upon them. Then a barrage of enemy rocket shells exploded into life above and before them.