There are no Borg in this book! I can't tell you what a relief that is, after the Borg-heavy TNG relaunch, and the depression-fest that is the Destiny triology. I don't even remember the Borg getting a mention in Treason (which does make it a bit difficult to place whether the story takes place pre- or post-Destiny - the general positive vibe of all the characters makes me think pre-Destiny).
Mackenzie Calhoun and his oddjob crew are back, boldly stumbling into things they should leave well alone. The main focus of the plot is on Selar and her desperate attempts to stop the rapid aging of her son (caused by his hybrid Vulcan-Hermit perantage). In trying to help Xy she makes some bad decisions and leads the Excalibur crew into an encounter with a threatening new species.
Peter David's writing is as good as ever. He remains very easy to read and mixes some dark and heavy stuff with light humour. Soleta and Calhoun are, as ever, particularly funny - especially in their scenes together. This book is an entertaining read by itself and seems to serve as the first part of a new Excalibur adventure. Certainly the final chapter points to something much bigger and more sinsister than even the (pretty far reaching) events of the main story indicated. I can't wait for the next part, and only hope it won't take as long to get here as Treason did.
A minor gripe: by now New Frontier has so many characters that some start to seem superfluous. We have the crews of both Excalibur and Trident, not to mention Kalinda, Xyon, the Thalonian guys, Shelby, and Soleta's lot. This book includes them all, but the net result is that everyone has very little to do unless they're Selar. Some characters appear seemingly to set up arcs for later stories, rather than to contribute to the plot of this one (Lefler, I'm looking at you).
Despite that I would recommend this book to anyone who is a fan of New Frontier, The Original Series (Calhoun's still doing his best to out-Kirk Kirk), or Trek Lit in general. Definitely if you're as tired as I am of the Borg.