Kirth Gersen is still the central character in this novel, is he really becoming the killing machine? Can he remain a normal human being and continue his quest for revenge? To younger readers used to much thicker novels, I would say that this is really a sub-novel of the Demon Princes book and if you read all five in the series it's still only about half the length of a Brandon Sanderson novel. It does have some of the old fashion tropes, damsel in distress and secondary weak female characters but in the early '60's when this was written, strong female characters were not part of SF.

This series is one big novel, they just couldn't publish giant SF novels in the early 60's. So read them in order!