The Face of the Unknown is a follow-up to the classic Star Trek episode "The Corbomite Maneuver", indisputably one of the greatest episodes in the franchise's 50-year history. Its successful combination of mystery, deceit, and delight make that episode particularly rewarding.
In this novel, set not long after the close of The Original Series' final episode (but just before the beginning of The Animated Series), in the latter half of the Enterprise's five-year mission, Kirk and crew receive a distress call that eventually leads them back to the infamous orb-ship of Balok from "The Corbomite Maneuver". Balok, however, is missing, and the First Federation (his home) is under threat from an ancient menace. What follows is a highly entertaining combination of mystery and deceit, making this book a delightful read.
The author, Christopher L. Bennett, is clearly a master of Star Trek lore, as the references to canon are knowledgeable, well-timed, and apropos. He is also deft at employing language to convey the familiar voices of our interstellar heroes, and that same linguistic adroitness lets him immerse the reader both in the expansive, awe-inspiring vistas of strange new worlds and in the vicissitudes of thrilling escapades.
If you're a fan of Trek, this is a very fine stand-alone novel -- highly recommended!