Leonard Marnham is "The Innocent" of the novel, a Post Office engineer who is employed by the Americans to install monitoring equipment in the tunnel they are building specifically to tap the Russians.

Ironically, Leonard lives in an apartment above one occupied by a rather stuffy character named George Blake, who was a Soviet agent imprisoned in the 1960s, and who escaped from Wormwood Scrubs.

The novel neatly intertwines fictional meetings between the two men, and one of Blake's most notorious betrayals is given a new slant by Leonard's foolhardy act.

Leonard, exhausted and in shock, wanders through Berlin with the heavy cases trying to find somewhere to leave the body parts, but gives up and returns to his flat with them.

Then Leonard runs into Glass, who admonishes him for removing equipment from the workplace and forces him to return the cases to the tunnel, driving him there himself.

The novel unravels Leonard's "innocence" in a deceptively comic fashion: the young Englishman, bumbling along, out of his depth, enduring jokes and insults from the Americans, suddenly finds himself at the abyss of fear and terror, where betrayal becomes easy.

[2] Michael Wood of the London Review of Books discussed the Gothic literary mode and wrote that "McEwan’s great gift is for getting his characters onto this level of experience by the most casual means."

Wood stated that the connection between Leonard's work and personal life gets too unsubtle, but praised the precision of McEwan's portrayal of emotion, billing the novel as "a haunting investigation into the varied and troubling possibilities of knowledge.”[3] Joan Smith referred to the novel as "far and away McEwan's most mature work" and "an outstanding achievement".

[4] A writer for Publishers Weekly argued, "Though its plot rivals any thriller in narrative tension, this novel is also a character study--of a young man coming of age in bizarre circumstances, and of differences in national character: the gentlemanly Brits, all decorum and civility; the brash, impatient Americans; the cynical Germans.

Although he praised McEwan's account of the building and installation of the communications tap as "taut and exciting", he said that the story of Leonard and Maria "gets out of hand" when her husband appears and that the ending, "after so much tension, [...] seems lackadaisical and routine.

The Berlin of McEwan’s novel is scented with the real thing, the diesel fumes and beery scents and the Wurstwagens and the bracing Berliner Luft, the air of Berlin.”[8] In a 2014 article for The Irish Times, Eileen Battersby praised the novel as "an interesting study of distrust" and one of McEwan's three best books.