It’s a rite of passage for young novelists to tackle rites of passage: the sun-dappled, backward-glancing, coming-of-age fable is as regimented and routinized as any lean-boned crime thriller or bulky, mock-Victorian doorstop. There is currently no shortage of such books, and there won’t be so long as the form retains its basic, elemental appeal, which is to chart the journey from innocence to experience in diverting, tactile detail.

At first, Eliza Robertson’s debut novel seems representative of its subgenre to a fault. Its opening section is titled “Beach House,” recalling countless other books (Canadian and otherwise) that use vacation homes as cozy, secluded crucibles of personal growth. The protagonist is a prepubescent girl feeling her first stirrings of attraction (for her 11-year-old stepbrother, who’s taken up residence in her family’s summer home). The water pounds against the surf; childhood’s end approaches; the island air is thick with pheromones and portent. It’s a fine line between archetype and cliché, and even an attentive and sympathetic reader could be forgiven for thinking that Robertson is toeing it a bit recklessly, on the verge of toppling off entirely before she’s even got started.

Happily, this does not prove to be the case. Demi-Gods is a resolutely sure-footed piece of writing, moving with fleetness and agility over its chosen terrain. It’s the work of a writer who knows how to pace herself – when to sprint and when to hang back. The familiarity of the setting, meanwhile, becomes a tool in the author’s arsenal. Robertson – whose 2014 story collection, Wallflowers, was extravagantly praised by critics – is a landscape artist with the signal ability to re-map spacious exteriors into teeming headspaces.

“I was scared to find what lived under there,” recalls narrator Willa when her new step-sibling, Patrick, invites her on an outing to an abandoned rowboat stowed down the road from the cottage. “I didn’t mind snakes if I couldn’t see them, but worried they would shoot from the grass up my ankles.” The sexual innuendo here is only barely submerged, and by the end of her lakeside adventure, Willa has been viscerally initiated into a realm of abasement and embarrassment that she recognizes clearly yet nevertheless pursues as she ages into a teenager and then a young woman.

Even for a deliberately slender novel, Demi-Gods is light on dramatic incident, driven instead by achingly plausible pathology. Patrick’s near-sociopathic diffidence obviously means trouble – a child psychologist would have a field day with this character – and yet he has a hypnotic effect on Willa, who is otherwise self-possessed and perceptive. She sees the world around her clearly: her blind spot is Patrick. We are privy to her observations about the cracks in her mother’s relationship with Patrick’s father (a perfect, miniature portrait of weakness masquerading as authority) and her older sister Joan’s near-flawless beauty-queen facade. It’s a subtle point that Willa’s near-fetishistic tendency to visually dissect the people around her – breaking them down into their component parts, with a special focus on lips and mouths – is a mirror of her own bodily self-consciousness.

There are other sly doubling tricks. The way the action shifts from B.C. to California adds a thin but substantive layer of cultural commentary as Willa reflects on the minute differences between the west-coast Canadian vacation spot and its American doppelgänger (the meditations on coastal living are another of the novel’s structural devices). Joan’s less furtive, officially sanctioned romance with Patrick’s brother, Kenneth, allows Robertson to further stretch the implications of a quasi-incestuous scenario while also keenly observing the operation of sisterly dynamics. The relationship between Willa and Joan doesn’t simply reflect the competitive give-and-take of so many all-in-the-family dramas; because Robertson is an empathetic writer, she strives instead for a dynamic that suggests mutual devotion occasionally shaded by wariness.

These faint, suggestive resonances hold the narrative together as it drifts forward through a decade of family parties and clandestine, unsavoury encounters between Willa and Patrick that keep deepening in perversity. These culminate in an extended adventure aboard a yacht that evokes the rowboat from the opening passages (yet another twinning motif).

Miles offshore and below decks, the action becomes pressurized as in a good thriller, and gets downright harrowing in the home stretch – a development that Robertson manages with the same apparent effortlessness as her scenes of landlocked frustration and yearning. Even when the violence bubbles to the surface, there’s never the sense of a writer straining for effect, and the high-end literary quotations that Robertson uses to frame the narrative – from Frances Leviston and Jorge Luis Borges – are skilfully integrated with her own themes and imagery instead of simply resting on top like adornments.

The Borges quote, taken from The Book of Imaginary Beings, promises that “a day will come when the magic spell will be shaken off.” Readers who allow themselves to get fully caught up in Robertson’s dense, disturbing prose may wonder how long it will take to free themselves from this novel’s own thrall