There is a limit to how perfecta counterfeit can be—a limit that cannot be passed withoutan odd phenomenon setting in....
followed them in, closing and locking the door behind him. They crossed quickly through the small building to an open wall portal at the far end. Beyond the portal a large, brightly lit room was visible, comfortably furnished, windowless. Between that room and the shed the portal spanned a distance of seven miles, a vital point in the organization of their escape route. If they were traced this far, the trail would end--temporarily, at least--at the ranch.
They stepped over into the room, and Rane Rellis pulled down a switch. Behind them the portal entry vanished. Back in the deserted ranch building, its mechanisms were bursting into flames, would burn fiercely for a few seconds and fuse to dead slag.
* * * * *
Rane said tightly, "I feel a little better now ... just a little! The Fed agents are good, but I haven't yet heard of detection devices that could drive through five hundred yards of solid rock to spot us inside a mountain." He paused as a tall girl with black hair, dark-brown eyes
This is a fairly entertaining story up until the end - at which point it falls off a cliff.
Aliens bent on destroying the human Federation are foiled by their own devices. Ho-hum.
It took a few pages to realize that the good guys were actually bad guys. An alien invasion story with spies so perfect they almost fool themselves.