It seemed to be following an invisible trail.

One evening after they left the road, the invisible trail failed.

An unconscious sigh escaped her as she followed him along the invisible trail only he could detect.

All day we had followed a nearly invisible trail.

So by carrying around your high-tech phone, you may well be leaving an invisible digital trail.

She continued away from the house following an invisible trail.

They would thus provide a clear but conveniently invisible trail to follow out of here when it was over.

Turning first this way and that, as if negotiating an invisible trail, he urged his starahk ever upward.

David led her quickly in the darkness, finding footing on the almost invisible trail without hesitation.

The other farcaster was somewhere near but the blizzard made anything off the trail invisible and inaccessible.