"Do you have any clues at all to who these unknown powers might be?"

Unexpectedly the Earth had gotten involved in the middle of a conflict between two unknown powers.

Her tale also suggests that the shoes are capable of time travel and unknown power.

Do you think they have some psychic power unknown to us?

An unknown power had brought her ship and crew halfway across the galaxy.

Trade was the strong man that broke it down, and raised a new and unknown power in its place.

Some unknown power carved them into her flesh, but she cannot remember the event.

Some power unknown to men was making it move.

As the men faced each other, the air thickened with unknown power.

Still, the glass ring held an unknown power; of that she was certain.