"Maybe I'll understand enough to get us through the night."
Bram seemed to gather himself. "Very well. This must you know....
"I am an agent in the service of the Great World. For centuries we have waged war against the Niss, evil beings who loot the continua. They established an Aperture here, on your Earth. We detected it, and found that a Portal could be set up here briefly. I was dispatched with a crew to counter their move—"
"You're talking gibberish," Tremaine said. "I'll pass the Great World and the continua ... but what's an Aperture?"
"A point of material contact between the Niss world and this plane of space-time. Through it they can pump this rich planet dry of oxygen, killing it—then emerge to feed on the corpse."
"What's a Portal?"
"The Great World lies in a different harmonic series than do Earth and the Niss World. Only at vast intervals can we set up a Portal of temporary identity as the cycles mesh. We monitor the Niss emanations, and forestall them when we can, now in this plane, now in that."
"I see: denial to the enemy."
"But we were late. Already the multihedron was far advanced. A blinding squall lashed outside the river cave where the Niss had focused the Aperture, and the thunder rolled as the ionization effect was propagated in the atmosphere. I threw my force against the Niss Aperture, but could not destroy it ... but neither could they force their entry."
"And this was sixty years ago? And they're still at it?"