This is book 2 of the "Subspace" series.

This note contains spoilers for the book.

I don't seem to have read this since I started booknoting; but this is catchup posting on kind of a reading binge, so I'm not up for much insight at the moment, either.

The sequel to Subspace Explorers (#7). This was a fragmentary manuscript, which survived only in editorial files and was discovered quite late. Lloyd Arthur Eshbach, who had seen the manuscript and corresponded with Smith about it, undertook to complete it. There are significant ways it doesn't feel Smithian, but they go through the whole book, not just the last part, so they're probably part of the Smith part (in other words, LAE probably isn't responsible for the ways I feel this book is weak). It wasn't published until 1983 (Smith died in 1965), and so far as I (and the ISFDB) know has had only the one paperback edition.

The Deston's and company discover the cause of the Zeta charge, and why spaceships very occasionally disappear—they're encountering countermeasures installed in second space, where the passage of the ships is causing terribly damaging X storms.

This second space has a very nasty, autocratic government, lots of blood-sports (but mostly fair gladiatorial fights in the arena, not the highly slanted things and mostly not the mass slaughter things from our own bad cultures), and execution by torture as a frequent part of life (when one becomes "eaglemeat", ones bones are broken and one is then put out alive for the large carrion birds to devour). But except for the Garshans, their psiontists are good guys, and peaceful contact is made, things are worked out, and the Garshan treachery is blocked (and the Garshans exterminated).