By Clea Simon

This hybrid narrative laces romantic adventure with a bit of horror, the supernatural, and mathematical derring-do—all within an increasingly realistic depiction of the times and of the people who survived them.

Nonesuch by Francis Spufford. Scribner, $41, 496 pp

Francis Spufford’s Nonesuch starts out as a delight, the kind of heady historical fiction that has readers checking hemlines and dance trends for accuracy. Where the story ends, however, is both darker and deeper, making for a thought-provoking and surprisingly poignant read.

It is 1939, and London is holding its breath, waiting for the Blitz to begin, when a headstrong office clerk in a silver bias-cut dress (“mermaid close”) whisks away an admirer from a malevolent upper-crust beauty at a Soho club. That clerk, Iris Hawkins, turns out to be far more than the “suburban slut” she first appears to be. As becomes clear when her aptitude for economics is pitted against John Maynard Keynes’s at another party.

What she doesn’t know, however, is that Lady Lalage “Lall” Cunningham—the posh “china doll” whom she bested for Geoff Hale, Iris’s would-be beau—is not only allied with the British Fascists but also has connections to a magical cohort of immense power. Before long, the meaty romance–mean-girl competition has turned into a speculative mashup of historical and science fiction, pitting its complex and believable characters against one another in a compelling, if fantastic, tale.

The resulting romance between Iris and her at-first innocent admirer, a BBC engineer, matures into a heartrendingly believable relationship, but the conflict sparked by their first encounter quickly grows from the personal to the political, as Iris and Geoff uncover a plot to travel back in time and assassinate Winston Churchill, all but guaranteeing British capitulation to Hitler. Luckily, Geoff has a strong grasp of non-Euclidean geometry, and, between his brilliance, Iris’s tough-minded approach, and a bit of mystical guidance from Geoff’s scatterbrained father, the two go on the offense as the Blitz begins to ravage London.

Part All the Light We Cannot See and part A Wrinkle in Time, this hybrid narrative laces romantic adventure with a bit of horror, the supernatural, and mathematical derring-do—all within an increasingly realistic depiction of the times and of the people who survived them. Iris, for example, is a formidable character, driven by dark motives that aren’t revealed until the book’s end. Spufford uses her to highlight the sexual hypocrisy of the era, perhaps going a bit too far with frequent (PG-rated) references to masturbation. But her clear-eyed take on the double standards of her world not only sets her apart but also plays into the upper-crust Lall’s intrigue (and eventual unveiling). The sexism of her professional world—especially at the stock brokerage where Iris works—is a given, another hurdle for this hard-minded heroine to leap.

With his lushly layered prose, Spufford recreates not only the background but the atmosphere of 1939 London, rich with anticipation as well as fear: “The August sky was furrowed with vibrations, but such fine ones, such fast and delicate oscillations, such minute needle point jittering of the fabric of empty space, that she would have needed to be an organism made of something finer than flesh and blood to feel the quick waves moving,” Iris observes. “Twist that dial. Between the bands of crackle were flying voices in all the languages that filled the sixteen skies of Europe, and skimmed more weightlessly than midges over the waters of the Rhine and the Danube and the Thames and the Volga.”

Soon Spufford replaces this heady ebullience with the lived-in exhaustion of the Blitz. Through Iris we are given a visceral sense of how, between the lack of sleep and running water, rationing, and anxiety, the residents of London were so worn down that peace at any price might have seemed reasonable—at least if magic weren’t an option. But in Nonesuch it is, and once Geoff and Iris decipher some of its rules (which include freeing angry, imprisoned angels), the book leans into its science fiction mode.

What Lall intends to do, the couple learn, is reach Nonesuch, a kind of magical middle ground from which history can be changed (think of the Woods Between the Worlds in The Chronicles of Narnia). Geoff’s engineering brilliance—he’s at the forefront of the television age and soon goes off to work at a Bletchley Park-style research facility—comes into play. But it is Iris who is required to put their plan in action. To stop Lall, she must navigate a treacherous trail that is only accessible during the dark of the moon, stretching the duel out over months of exhaustion, when she is “so tired that her reactions to everything were muffled… The sirens would go again in a couple of hours, and all she wanted to do before that was to fall over and close her eyes.”

London in wartime is a world that Spufford knows well. He has already published Light Perpetual, a more realistic fictional account of children killed during a 1944 bombing, where the author imagines the lives that they lost. Setting real historical tragedy against fantasy might seem like an avoidance mechanism, an emotional flinch from pain. In Spufford’s hands, however, the approach effectively highlights the unreality of such overwhelming horror. In Nonesuch, the intrusion of the supernatural presents itself as a reasonable alternative. If we are not watched over by angels, what sense is there in the world?

It is worth noting that Nonesuch trips up at its end, however. A very late revelation ties some threads together and unravels others, leading to an unsatisfying, if in some ways inevitable, conclusion with a “to be continued” tacked on. The publisher says a sequel is planned for next spring, which could set this right. At the very least, it promises to prolong this otherwise highly enjoyable outing.

Clea Simon is a Somerville resident whose latest novel is The Cat’s Eye Charm (Level Best Books).