Mr. Gardner's Understrike is his second novel about the British Security Agent Boysie Oakes, and this time he is involved in the test firing of a lethal missile from an American submarine, with the Russians the baddies. Boysie Oakes, as before, is depicted as lovably human—i.e., keen on girls, frightened of pain and death, neurotically forgetful, careless and even stupid, but somehow winning through. I find this portrait too sophisticated to be gripping: the indulgent smile which I think the author means one to wear about Boysie to the point of faceache, prevents me from gasping or stretching my eyes, which is all I want to do when I read this kind of book. It is all rather an indoor romp—like playing cowboys in the squash court. (p. 727)

Elizabeth J. Howard, "The Strange Adventure," in The Spectator, No. 7145, June 4, 1965, pp. 727-28.