There is a man and a woman traveling to an alien planet, and along the way the woman's soul begins powering the ship.
Also, on the way to the alien planet, an alien set of "lights" that exist only to do complex dances in the sky take the man & lady's souls on a dance. Plus, on the alien planet, there are a couple lifeforms, one of which are the "workers" that cannot live unless they are given something to do.
The man takes one of the workers on the ship back to Earth, and tells the worker to find a key. The worker spends the whole trip looking for a key, and then dies.