Mark Travers hoisted himself up from the floor. He leaned against the supply locker, rubbed his aching jaw where the big man's fist had just landed, and grinned ruefully. The big spaceman didn't grin. He faced Mark straddle-legged and snapped, "Who are you?" "Mark Travers." His smooth gray eyes surveyed the man's bulk. He thought he could handle him, but filed it for future reference when he saw the neutro-gun in the other's fist. "Travers, eh. A blasted stowaway! You come aboard at Marsport?" "