Challenger - Diane Carey

Far from the reaches of the Federation, the Starship Enterprise has been guiding the development of a once obscure colony planet upon whose fate the future of the galaxy may now depend. The Enterprise has been the sole representative of the Federation, fighting a constant battle to protect the colonists from enemy aliens and others who may have their own designs on the colony world.
Now it is time for Captain Kirk and the Enterprise to turn the guardianship of the colony over to another ship and crew. Arriving in the midst of a deadly attack on the settlers, the new ship is destroyed. With the Enterprise occupied in fighting off a new and powerful enemy that threatens both the colonists and their enemies, the future of the planet lies in the hands of Commander Nick Keller, first officer and ranking survivor of the decimated crew. Marooned and - at first - alone, he must find a way to complete his original mission and come to the aid of the Enterprise in what might be its most desperate hour.