The Greater Good is the latest volume of the Ciaphas Cain series. Set in the Warhammer 40K universe, it follows the adventures of the titular Commissar. Ostensibly a political officer, Ciaphas Cain is a somewhat cowardly figure who continually finds himself in horrifically dangerous situations against the Imperium's worst enemies.
Managing to survive through a combination of luck and a keenly-honed sense of self-preservation, Cain finds himself with a mostly-deserved reputation as a galactic hero. Which, of course, means he's the first called upon whenever things go to hell. It's a neat little premise for a book series and Sandy Mitchell (the pen name of writer alex Stewart) does an excellent job telling always-entertaining stories about Cain's near-brushes with death. Unfortunately, after nine books, the premise is running a bit thin.
Part of this has to do with the de-emphasizing of the secondary characters who accompany Cain on his mission. While we know Cain will survive to become an old man due to the framing narrative, the others provide a sense of danger as well as character arcs that make the books enjoyable.
There's also the fact the enemies we've seen Cain deal with are becoming a bit stale. We've seen Cain deal with Orks, Tyranids, and Necrons on numerous occasions. The change to things like Chaos forces and heretics is something I think we need more mileage from. Likewise, I'd like to see Cain deal with Eldar and Tau. I was hoping this would be a book which dealt extensively with the latter as I'm quite a big fan of the latter and seeing Cain play off them was something I hoped to see. Sadly, this is not the book for that.
The Greater Good has the premise of Commissar Cain participating in a war for an inhabited world being fought between the Imperium and the Tau. Halfway through the latest of their battles, he's contacted by the Tau who want to make a armistice. A swarm of Tyranids is coming to threaten all of them. Making an alliance, Cain also discovers a secret Techpriest project which threatens to either save or destroy all three sides.
I enjoyed the first half of the book a great deal because watching the Imperials deal with the Tau and, especially, converted humans was quite entertaining. I was hoping to see some of Cain's legendary womanizing affect his relationship with their "diplomat" but, sadly, this didn't happen. The second half of the book was less interesting to me as it was mostly devoted to combat against the Tyranids. The battle scenes were entertaining, don't get me wrong, but I would have preferred to get more Tau-Cain interactions.
In conclusion, The Greater Good was an entertaining but not especially memorable entry into the Ciaphas Cain series. There's not much in the way of character development or interactions we haven't seen before. The best moments in the book are those early encounters with the Tau as well as a surprising Genestealer infiltrator's final moments. It's a fun novel but nothing which is a must have. I'd recommend the other volumes in the series over this one for the "Best of Ciaphas Cain."