Chaining the Lady by Piers Anthony

her.
    â€œNow it seems the entities of Galaxy Andromeda have perfected a technique through which involuntary hosting is feasible,” Fltosm continued. “They are able to transfer their high-Kirlian auras into lesser-Kirlian hosts without the prior consent of those hosts. And they have done so, taking over a number of our most sensitively located entities. We call them hostages: involuntary hosts. There is no way to discover a hostage except by aural equipment. Thus we do not know which of our government officials are hostages, for we cannot require them to undertake aural verification without alerting them to our suspicion. It is an uncircular situation.”
    â€œAgreed,” Melody said.
    â€œI'll say!” Yael exclaimed. “Can't test the spies without making it worse.”
    â€œSo we have initiated a quasi-legal program of hostage identification and research. This is not under the direction of our governing ministers, because we know that at least one of them is himself a hostage. But our program is essential to the welfare of our segment and our galaxy. If the Andromedans infiltrate and conquer us, our entire galaxy may perish—literally. For they mean to draw away the binding energy of our atomic structure to facilitate the power required for their advancing civilization, and our very substance will disappear in the course of a few thousand years.”
    Melody understood. She believed the Polarian, and knew now that it was no idle reason that chained her to this host. The survival of her galaxy was at stake. She would have to do what was required, however inconvenient it might be to her personal life.
    â€œWe operate through the Society of Hosts,” the Polarian went on, “because they alone possess the aural expertise to assure the absence of hostages in their own ranks. This is why it is necessary for all our operatives to join the Society. Aural verification is an unquestioned requirement for entry. No suspicion attaches. The Society has undertaken research into hostaging, but has been unable to duplicate the Andromedan technology. Perhaps if a living hostage could be studied—but we dare not touch any that we know of on this planet, because that would give away our knowledge of the Andromedans and precipitate an immediate crisis that could cost us the war.”
    The Colonel smiled approvingly. “Not only are you sounding like a Solarian now, you're talking like a military man.”
    â€œAt times thrust has its applications,” the Polarian agreed, glowing with distaste. “But circularity will be required for the resolution.”
    â€œAgreed,” the Colonel said. “Sorry I butted in.”
    â€œIt is the nature of your kind,” Fltosm said generously. Then, to Melody: “Society calculations indicate that a hostage can be reclaimed through our existing technology, provided the hostage is rendered unconscious and laid under siege by a completely superior aura of the same family. Perhaps a different aural family would succeed also; that is less certain. You understand how auras exist in related types, apart from intensity, some being compatible and others so diverse as to be incompatible?”
    â€œYes,” Melody said. “This accounts for what was historically known as 'instinctive' attraction or repulsion between given entities. A parallel could be made to your Solarian or Polarian blood types.”
    â€œYes. But even with a reasonably close match, the margin of superiority would have to be at least four to one over the besieged aura. The technology of Andromeda has evidently abated this necessity, but we of the Milky Way must resort to comparatively crude force. Therefore–”
    â€œI believe I understand you at last,” Melody said. “You have located a hostage whose controlling aura is of my own aural type, too high for any other entity to overwhelm.”
    â€œPrecisely. It is a female hostage governed by an aura