This is a fun story. It starts with a classic Wolfe pun:
"Three with egg roll.... Soon to be four without...". Then we find out there are three crewmembers on a ship called Egg, which is rotating to provide artificial gravity. Almost as good as the start of Eyebem. Also, there's a macaw named Polyaris, which is a excellent pun on Polly (as in, "want a cracker?") and Polaris, the north star.
We also get some lovely descriptions of the crew's view of space through the windows.
Then we dive into Wolfe's look at shadow matter, a "dim insubstance [lovely word] felt only in its mass and gravity, its unseen heaviness." I think this is Wolfe's take on dark matter and dark energy; this story was written in 1987, so I'm guessing the idea of matter/energy that doesn't interact with the electromagnetic force (dark matter/energy) to help account for the added mass of the Universe was out there for Wolfe to explore, The crew can only "see" the shadow matter by mapping its gravitational pull and visualizing it via computer; I assumed similarly to how we use infrared cameras or X-rays.
Then one of the crew says he can see the shadow matter, because he died on the trip out, and suddenly either he's gone crazy or we are on a trip to the Underworld. Absolutely great stuff that all fits into only 3 - 4 pages.
One of the crew is a robot or maybe cyborg (he describes himself as "largely inorganic"), which leads us back to Wolfe's favorite questions about sentience and beliefs.