For King & Country by Robert Asprin, Linda Evans, James Baen Page B

Briton Lords of Battle."
    "Quite," she smiled. "I see you're a well-read man, Captain Stirling. Mind your manners, Cedric."
    Banning laughed, clearly unrepentant, and lifted his glass in a mock salute.
    Mylonas cleared his throat. "Yes. Well. If you project yourself into
a
past, along the fractural plane that resonates most closely with your present, you then find yourself in a new present, with an infinite number of potential futures stretching out before you. Should you take an action contrary to the ones taken on your plane of origin, call it Fractural Prime, then your consciousness will slide into a
different
fractural resonance, perhaps close to your Prime, perhaps not, depending upon the magnitude of difference between the two."
    "Then it isn't changing history at all, is it?" Stirling's mind had filled with images of vast sheets of multihued crystal fragmenting and crashing into one another, until the universe resembled a pile of shattered quartz, pulverized under a geologist's hammer. The longer he thought about it, the more the image disturbed him.
    Mylonas sighed. "It's a bit of both actually. It isn't as simple as you imagine."
    "What do you mean by that? Either it is or it isn't."
    "Not in fractural physics. The key word is
resonance.
If you switch from one fractural plane to another, the law of conservation of energy—among other things—
requires
a transfer of resonant energy between them. If the two resonances are sufficiently dissimilar, a dissonance is created. An energy embolism, if you will. Depending on how far back the dissonance occurs, it may have either negligible or very serious consequences in your Fractural Prime. The resulting embolism may produce a minor bruise, or it could produce catastrophic damage."
    "Catastrophic?" Stirling blinked. "What, exactly, are we talking about here? What scale? Do you mean the traveler's energy pattern is violently disrupted? As in, fatally? Or do you mean something else? Something... worse?"
    "That," Mylonas said tiredly, "is precisely what we do
not
know. The traveler could die, yes. Maybe. Unless the dissonance only affects things
after
the energy pattern's shift between planes.
You
might be spared, while everything else fractures around you. If the dissonance is set up in the new fractural plane, you might destroy the future of that plane, rewrite it, so to speak. You'd start with a clean slate, from your perspective, although you might well be killing off billions of people in the secondary plane's future. No way to tell, of course, subjectively, from the traveler's viewpoint.
    "But suppose the dissonance affects the old fractural plane, the Prime you originally came from. This one." Mylonas rapped bony knuckles against the tabletop. "What do you have, then? Your action in moving from Fractural Prime to Fractural Secondary destroys both the present
and
the future of your plane of origin. Shatters it to bits, in fact. By setting up the dissonant energy pattern in the past of one fractural plane, you utterly destroy at least one future, possibly both. Not a terribly attractive situation for scholars, but
frightfully
attractive to some madman bent on vengeance. Or a terrorist bent on political blackmail."
    "Dear God," Stirling whispered, staring into Mylonas' haunted eyes. "You're talking about the murder of
billions
of human souls!" He didn't know precisely how many people there were in the world, but it was an appalling number to snuff out in one fell swoop.
    "Yes." Mylonas swallowed. "That is the reason the Home Office insisted on sending a chap who understands counterterrorism."
    Stirling struggled to reorder his entire view of the tactical situation. Indeed, his view of the entire universe. He glanced around the table, finding stunned eyes and expressions of rising horror. Clearly, none of them had fully grasped the project's lethal potential until now. Unless, of course, one of them
was
a terrorist, someone who would have realized exactly what could be