Therefore I decided it was best to attack the unknown forces.

An unknown force had tried to take possession of his mind.

Some unknown force has been involved in changing the trajectory.

It might well be that she did have command over some unknown force.

To Betty, it seemed as though she were being carried through the air by an unknown force.

Outside, he is drawn back into the ship by an unknown force.

That we must get from this place filled with a play of unknown forces was the first thought in my mind.

Maybe they did think that he'd been taken by some unknown force.

How frequently were these unknown forces found to be acting?

We want you to protect him from forces known and unknown.