Robots were infiltrating the Federation. Someone was kidnapping people and substituting indetectable, synthetic imitations. Somewhere, aliens were studying the Federation, using techniques beyond human developments. The trail led back to Cerberus and the Lord who ruled that planet.
Cerberus, however, was one of the Warden Worlds - and those Worlds were the untouchables of space. There a strange microscopic lifeform invaded all matter, and anyone so infected died on leaving those Worlds. Men could go there, but never return.
But the Federation had its own techniques. they took a criminal named Qwin Zhang and stripped her mind of all memory and personality. then they poured into that empty receptacle the full mind of the Federation's best operative. They exiled her to the prison world of Cerberus. the mission: find the lord who ruled, kill him, and take over.
Too bad there were things about Cerberus they couldn't know!
The Federation put the masculine mind of their greatest operative into the female body of Qwin Zhang. His/her job was to find the Lord who was working with enemy aliens and take control of the whole planet. And, of course, report back to the alter ego of his mind - by some means unknown to Zhang.
Being female and naked on a planet where utter ruthlessness was the major survival factor was a problem at first. But then he learned that on Cerberus, exchanging bodies was made by routine by the symbiont bug - consciously or unconsciously. He could become male again - so long as he kept control.
He could also become immortal through such bodily exchange. And what kind of a damned fool would put duty to the Federation above a chance to gain lordship of a planet - and immortality!