The Enterprise receives a distress call and responds to find the planet taken over by an alien race from another universe. Sulu, Kirk and Spock are in mortal peril and the Enterprise herself my plunge into the atmosphere killing all. There are the usual shenanigans and all ends well.
There are so many things wrong with this book (I wasn't aware that aliens from another universe would speak Federation Standard, but it seems they do!!) that I will only mention one: Characterization.
Uhura is in charge of the ship and has to face off against the belligerent alien leader. Yes!!! I thought. Uhura is going to bat her lovely brown eyes at this guy, charm him and before he knows what hit him the Enterprise will win the day. Well, no. She says "No dice" "Save your breath mister" and "I have your number." I've always considered Uhura a true lady with a spine of steel, not a 50's tough guy. None of this sounds like her. And at this point, although the aliens have not been friendly, it could all be a big misunderstanding. Why would she risk antagonizing these folks? The "true" Uhura only breaks through a few times and never when the things are rough.
She has to save the Enterprise, Kirk, Spock and Sulu. The outcome is foreordained. Success is inevitable; we know the future history of these people. One way to make this story work would have been to introduce another character, take the time to make us care and put that character into jeopardy. The way I would have liked the story to go would have been to make the outcome dependant on forcing Uhura to compromise her values or to have her fail--turn the ship over to whoever is next in line. Her character could have grown by accepting sometimes you have to do what you have to or understanding what she can't do. To grow you have to face challenges and risk failure. In this book, there is no risk of failure; the challenges will be overcome no matter what Uhura does. There is no growth.
In the Trek novelverse, Uhura never gets a command as far as I can recall. Why not? (This cannot be because of sexism or racism, this author is clear that such things do not exist in the Federation.) There's a story to be told there, and this book could have contributed to that story. But the author chose to take the easy, boring route.
This is written competently. No grammar or spelling issues I noticed. I assume it's set in the 4th or 5th year of the mission.