Lone Wolf #13

"Come on," Wulff said after a while. "You can talk now. Tell me."
Díaz lay there. It would be interesting to study the psychology of a man who had reached absolute hopelessness, Wulff thought, but he did not have the time for that now. "Names and addresses," he said, "or I'll kick you again, and this time I won't go low."

Díaz began to talk. He told Wulff what he wanted to know, with admirable specifics. Wulff listened without comment. It was highly interesting. He would not have imagined, having gone this far in, that there was this much of a new echelon left. It just went to show you that enterprise was endless.
"All right," Wulff said when the man was finished. "Thank you very much." He leveled the gun at Díaz and shot him in the head three times. Then he put the gun away and went out of the room and started immediately upon his final mission...
The final, climactic conclusion to the Lone Wolf series, originally published by Berkley Books in the early 1970s under the name "Mike Barry."