Simon Mawer's new novel, "Tightrope," is a follow-up to his last one, "Trapeze" (2012), and continues the daring acrobatics of his wonderfully drawn Anglo-French spy, Marion Sutro. On her last outing Marion was recruited by Britain's Special Operations Executive and dropped into Nazi-occupied France to carry out a perilous mission. "Tightrope" takes Marion from the certainties of world war and plunges her into the uncertainties of peacetime, and later the Cold War.

Mawer entices us at the outset by having a character inform us that Marion is perceived by some as a heroine and others as a traitor. Thus snared, we read on to discover for ourselves how fine a line she has walked on the high-wire.

After being captured and tortured by the Gestapo, then sent on to endure "the purlieus of hell" in Ravensbrück concentration camp, Marion returns to England in 1945 and attempts to adapt to civilian life. But as the Soviet Union shifts from "brave ally" to "ill-defined menace," her former handler reappears on the scene and coaxes her back into the "shadow world."

In Paris and London, Marion becomes embroiled in an elaborate cat-and-mouse game of lies, deception and double-crossing. Mawer's fiendishly convoluted plot encompasses atomic secrets, Russian spies and romantic blasts from Marion's past. The stakes are raised when Marion is tasked with becoming a honey-trap to "turn" a Soviet agent. With so many people watching her every move, she starts to wonder whether she is truly in control or if someone else is pulling the strings. More critically, she comes to love her enemy, and when he entreats her to join him in exile she is faced with a moral conundrum.

British-born Mawer has excelled with another tangled, character-led literary thriller. His characters convince, from Marion's stolid ex-Spitfire pilot husband to her inscrutable quarry-then-lover to her oleaginous spy-supremo boss — a man who gets his own way by using "blackmail, glossed over with a thin varnish of flattery." But it is Marion who is the indisputable star turn, a woman haunted by history, torn by opposing loyalties yet determined to stay afloat.

Sam, the book's on-off narrator, who is smitten by her in adolescence and adulthood, sums her up best as being "courageous, independent, slightly bloody-minded, more than a little amused by the idiocies of others, disturbingly attractive."

The novel has a framed structure, with an 80-year-old Marion in the first and last chapters and the exploits of her younger self in between. Though an elegant design, it drains the narrative of some tension, as we know from the beginning that the main character survives. Similarly, readers expecting a female James Bond should look elsewhere, as Mawer favors more the intrigue, treachery and atmospherics of Alan Furst and Graham Greene.

Whether read as a sequel or a stand-alone novel, "Tightrope" is a perfectly poised balancing act. Here's hoping it's not the last we've seen of Marion Sutro.

Malcolm Forbes has written for the Times Literary Supplement, the Economist and the Daily Beast. He lives in Edinburgh, Scotland.