Errand of Vengeance: Bk. 3: River of Blood by Kevin Ryan
Captain James T. Kirk and his crew, new to exploring the galaxy, must learn some difficult lessons -- and things are not always as straightforward as they seem. At the very start of their five-year mission to explore the galaxy, Captain Kirk and his crew must balance the needs of the Federation to know what the universe contains against the perils they inevitably encounter on their expedition through space. Their ethos is one of non-interference, and every effort is made not to harm the things they have come to learn about. But in the process, they discover that sometimes the efforts they make to avoid doing harm can lead to the greatest harm of all.