Enigma

Merritt Thackery knew from boyhood that his only dream was to be part of the Unified Space Survey. He prepared himself with five years of training on an exquisitely boring space tug, and with a speciality in alien linguistics. When his chance finally came, he was more than ready. But even Thackery's boyhood dreams could not have prepared him for his final mission, beyond the borders of known space: To seek out an unknown enemy and win Earth's freedom at last!