Lensman Series by E.E. "Doc" Smith

Kim Kinnison, Number One man of his time, had faced challenges before—but rarely one as daunting as this. To him fell the perilous task of infiltrating the inner circle of Boskone, stronghold of galactic civilization’s most deadly foe. Kinnison had to become a local Boskonian in every gesture, deed—and thought. He had to work his way up through the ranks of an alien enemy organization, right into the highest echelons of power... moreKim Kinnison, Number One man of his time, had faced challenges before—but rarely one as daunting as this. To him fell the perilous task of infiltrating the inner circle of Boskone, stronghold of galactic civilization’s most deadly foe. Kinnison had to become a local Boskonian in every gesture, deed—and thought. He had to work his way up through the ranks of an alien enemy organization, right into the highest echelons of power. Then it would be he who issued the orders—orders that would destroy his own civilization.. less