Ordeal in Space

This was Lieutenant Mike Logan's chance—alone in space with the man he ached to kill. A man, bound and helpless, who taunted him, dared him, goaded him—knowing Mike had to bring him in alive!
A needle gun pointed through the cell bars at the hulking form of Edward Snyder, his blue-furred Moon mimic squirming on his lap. Behind it were the cold hands, cropped black hair, and bloodless face of Lt. Mike Logan. It had taken him three hours to slide past the guards of the transient prison. He would leave with the same efficient caution. But first he had to kill!
Snyder looked up and saw him. The flabby face twisted cynically. Something personal, Lieutenant, or does the gun make it official?
Ask your questions in hell, Logan grated. His angular length was bent; gray eyes bloodshot and he fought to keep them open. After two months of tramping over Pluto's ice cliffs, he had returned to Jupiter to find the odor of death and no rest.
A savage desire for revenge had driven him on until now he stood staring almost unseeingly at the killer. The needle gun would be silent and untraceable. You killed Johnny. This is for him.
Snyder shrugged beefy shoulders. I've killed many and life is cheap. I can't remember them all.
He was the last one, Logan choked. He was my brother— Something caught his arm in a vice from behind. A stab of pain shot from his wrist to his neck.
Sorry, Lieutenant, but I got to keep 'im alive, the voice of the prison guard broke in his ear. He felt the gun drop from his fingers and tried to break free. Through the bars he could dimly see Snyder's mocking smile. Then something struck him on the head and he slid a long ways down.
An hour later he stood at attention before the command desk of the Patrol's Jupiter division. His knees were weak, chills of exhaustion tracing his back muscles. He was washed up and he knew it.
I used to think I could count on you, Commander Bates stormed. Well, I was wrong. You're nothing but a damned gutless jellyfish. If it weren't for your record I'd have you cashiered here and now.