I had to rate this one as "Average".
I normally find Mr. Cox's work to be thoroughly engaging, entertaining and fascinating to read! But this one was a bit of a slog at times. It took me over a month to finish the book. I didn't dislike the book, but it just didn't capture me. I sometimes went days without picking it up.
I think this one came across to me as just a series of vignettes. Mostly separate stories with just a bit of a connected thread. The grand story didn't seem to me like it was all intertwined. I'm not sure that actually makes sense, but I'm also not sure how to describe it better.
I connected more to the Ryjo part of the story and I definitely understood that his character was having doubts about his mission, but there were also times that I just "yelled" at him "Dude! Figure it out! Listen to that conscience!" My favorite parts of the Chekov story were once he ran into Dise. I wish they had spent more time together and the book had explored that relationship more.
I think one of the big things that kept taking me out of the story was that I couldn't believe that the crew--and Sulu specifically--would not have noticed that something off about Chekov and that worries wouldn't have started to grow amongst them. It seems to me that no matter how much education Ryjo had in how to do Chekov's various jobs and how much he knew of Chekov's history, the personality just wouldn't be there. There would be both subtle and glaring tells that something wasn't right. Sure, how he interacted with Simone did set off a few alarm bells with Sulu, but that didn't really seem to go anywhere. But even outside of that, I would have to think there would be lots of examples of things that just weren't right.
I will say that I enjoyed a glimpse into another Enterprise-A adventure. As well, the story on board Copernicus was fun and I enjoyed the tension in that one. And, as I said earlier, I liked the time spent between Chekov and Dise. So, there was definitely good in here!
But, overall, this one just didn't hit with me. It wasn't a bad book. But, it wasn't as good as I had hoped.