Tom McCarthy: C

“ Sulphur,” she says. “Yes, we’ve got that. Potash… yes. Nitre?” Her finger runs up and down the rows of bottle-stoppers as though playing a glockenspiel. Serge feels a chemical reaction in his stomach, a kind of effervescent coupling and expanding of juices and elements. “Right,” Sophie announces. “We’ll do this one. Read me the recipe. Page eighty-four.”

She thrusts the book at him and starts laying out tubes, bottles, retorts and a gas burner. The Playbook’s cover has a flowery pyramid embossed on it. Serge flips it open, flips past “Properties of Matter,” “Adhesive Attraction,” “Impenetrability,” arrives at “Chemistry.” Hermes or Mercurius Trismegistus, minister of Osiris… alchemy… chemical combination, one or more substances uniting and producing third or other body different in nature from… Page 84: To return to…

“ ‘To return to our first experiment with the gunpowder,’ ” he reads, “ ‘take sulphur, place some in an iron ladle, heat it over a-’ ”

“Iron ladle?” Sophie says. “We can use a cup.” She roots around the work table, tips a bunch of fuses from a metal cup and, after wiping its interior with her fingers, decants clear liquid into it from a bottle. A sharp smell burns Serge’s nose, inside the bridge. Wrinkling her own, Sophie sets the bottle down, sparks up the Bunsen burner and holds the cup over it. “What next?”

“ ‘… over a gas flame till it-’ ”

“I’m doing that already, stupid. Till it what?”

“ ‘-catches fire,’ ” Serge reads.

On cue, the cup starts burning. “Oh, wow!” says Sophie. The flames are blue, not orange; they make her eyes, already blue, glow bluer and her teeth flare bluey-white, like patterned marble.

“We’re meant to pour it into a bucket of water,” Serge says, “but the room should be blacked out.”

“Well, we’ll skip that,” Sophie tells him. “What’s next?”

Next is an experiment with sulphur and dissolved nitre; then one with sulphates of potash and baryta; then another with nitrate of baryta and metal potassium. Serge reads directions from the Playbook; Sophie executes them, her face running red, orange, grey and blue again as each compound lights, flares or fizzles. When they come to heat up charcoal Sophie blows into the cup and they watch sparks fly out, the powder turning from black to red, then fiery white, before falling back grey and ashen, consumed by its own heat. As Sophie prods the ashes, Serge feels the reaction in his stomach again: a liquid flaring eating his own insides.

“Pearl-ash next,” says Sophie. “Read out the next passage.”

“ ‘If some more nitre be heated in a ladle, and charcoal added,’ ” Serge begins, “ ‘a brilliant deflagration (deflagro) occurs, and the charcoal, instead of passing-’ ”

“It’s ‘day-flag-row,’ stupid, not ‘der-flower-grow,’ ” she says as she holds the new concoction over the Bunsen flame. “Carry on.”

“ ‘-instead of passing away in the air… passing, passing away as…’ ”

The queasiness is spreading to his head as his own stomach deflagrates, something sour and crimson blossoming, expanding. He looks up. Sophie’s staring at him, static. Her whole face seems to have slowed down-slowed down and expanded too. Her hair has expanded outwards from her head, rising to stand straight up in the air. His gaze follows it upwards and he sees instruments rise and hover above shelves. They do this incredibly slowly, as though willing themselves upwards, through excruciating effort, millimetre by millimetre. A window breaks, with the same slowness; he watches each of its glass fragments separate from the plane around it. There’s no crash or tinkle; there’s no sound at all. Serge tries to ask Sophie how she can make her hair stand up like that, but finds that his words, instead of travelling out into the air, push back into his mouth and on towards his stomach. Now sound and speed return, first as an after-rush of air, then, emerging from within this, a high-pitched hum that seems to have been going for some time but of which he’s only now become aware. Sophie’s still staring at him. Her hair’s tangled and her eyes are wild. A gasp comes from her mouth; then another, then a shriek of pleasure. She shouts something to him.

“What?” he shouts back. The hum’s filling his ears.

“Expl-” she begins-but he throws up right then, on the floor. His puke is red, laced with a briny, effervescent silver the same colour as potassium. Sophie looks at it, then back at him, then shrieks again, her shoulders shaking as the shrieks turn into sobbing laughs that judder her whole body.

Their father opines later that there must have been some contaminant in the cup to cause such a violent explosion. He ventures, further, that Serge and Sophie’s extreme proximity to the point of detonation kept them from harm: had they been standing three feet from it, the force of the expanding air would have been enough to kill, or at least seriously injure, them. He plots diagrams showing the explosion’s vectors through the room-table to work table, to shelf, to window-and tries for several days to ascertain the exact nature of the compound inadvertently concocted by his children. Serge and Sophie, for their part, spend weeks, then months, trying to reproduce the blast. They use means more intuitive than their father’s-mixing elements together at random, heating, cooling and remixing them-but have no more success than he did. All they ever get are small-fry phutts and phizzes, unsatisfying placebos.

Sophie and Serge are educated together. Their tutor, Mr. Clair, is shinily clean-shaven, with sharp features and an aquiline nose down which he peers through metal-framed glasses as he reads dictations, eyes zapping from his paper to the children.

“ ‘Amund-sen’s last ven-ture, through the Northwest Pass-age, yielded little joy. It is to be hoped, by those that value con-quest of the earth, that his current one, to the anti-po-dean regions, will prove for-tui-tous. For those whose daily tra-vels take them no fur-ther than the slums of Man-chester and Glas-gow, it will be of scant conse-quence. The forth-coming coro-nation, simi-larly, will do little to put bread on ta-bles of the poor.’ ”

Serge gets stuck on words like “antipodean” and “fortuitous,” and even ones like “tables.” He keeps switching letters round. It’s not deliberate, just something that he does. He sees letters streaming through the air, whole blocks of them, borne on currents occupying a zone beneath the threshold of the comprehensible, and tries to pluck and stick them to the page as best he can, but it’s an imprecise science: by the time he’s got a few pinned down, the others have floated on ahead or changed their meaning, and “Manchester” ’s “chest” has turned into an old oak coffer, the king’s “coronation” into a flower, a carnation. While Sophie scribbles neatly and assiduously, and always faultlessly, inscribing each word as it emerges from Mr. Clair’s mouth, Serge, bathing in the phrases’ afterglow, usually gives up after a few lines and just lets the words billow around him, losing himself in their shapes and patterns, bright and alive in front of Clair’s grey skin.

When Mr. Clair arrived at Versoie House, one of the first things he unpacked from his trunk, alongside volumes by the likes of Morris, Bastiat and Weber, was a painting, which he hung carefully on the wall of his small room. Under interrogation from Serge and Sophie, who spent so much time curiously perching on his bed and window-sill that Maureen had to come and turf them out, he admitted having painted it himself. It showed, he told them, Venice: the intersection of two canals, a mooring jetty being approached by a small boat. Painting’s a big thing for him; he’s made it a large part of their curriculum. Here too, though, Serge is wanting. He’s a steady brushman, and has a good feel for line and movement, but he just can’t do perspective: everything he paints is flat. Mr. Clair’s explained the principle of it to him, its history, and what he calls its “use-value”; he’s shown him its mechanics, how to scale figures and objects so as to make them appear distant, how to make lines converge towards a vanishing point set within or just beyond the picture’s border and so on. But Serge just can’t do it: his perceptual apparatuses refuse point-blank to be twisted into the requisite configuration. He sees things flat; he paints things flat. Objects, figures, landscapes: flat. Even when Clair sits him down in front of reproductions of Giottos, Constables and Vermeers and orders him to copy them, the scenes accordion down into two dimensions, sideways-facing characters stuck straight onto squashed backdrops. On Tuesday afternoons, the slot Clair’s assigned to landscape painting, the children invariably head up to the attic, and Serge paints the estate from above: its paths, corridors and avenues all laid out in plan view. Sophie, meanwhile, takes a leaf or branch with her and copies it in photographic detail.