HBO’s COVID hit series “The Vow” unleashed what has become an almost insatiable appetite for cult documentaries — the more extreme, the more addictive. By now we are all but inured to the wild things people do to belong: drinking colloidal silver, getting branded, stalking their supposed “twin flame.”

Because Ruby Todd’s debut novel, “Bright Objects,” is loosely based on the Heaven’s Gate cult, whose members, with the help of phenobarbital, imagined they could hitch a ride on the tail of the Hale-Bopp comet in 1997, you might expect some of the same emotional pyrotechnics and bizarre antics you found in 2023’s hottest cult documentary series, “Love Has Won” and “Escaping Twin Flames.” Instead, Todd has chosen a quieter and more unusual route toward understanding the extremity of belief.

It’s 1997 in the small Australian town of Jericho. A newly discovered comet, St. John, is approaching Earth — its impending arrival summoning fevered responses from the town’s residents, most of whom are searching for outsize meaning in the sky. One of these searchers is Sylvia Knight, whose husband, Christopher, was killed by a hit-and-run driver two years earlier. Tortured by the fact that the killer remains at large and unwilling to live without Christopher, Sylvia has set a date for her own death.

Before she can carry out her plan, she finds herself torn between a surprising new lover, Theo St. John, the astronomer who discovered the comet, and Joseph Evans, a local mystic with increasingly fatalistic notions about the comet’s approach.

At the outset Sylvia tells us that she has died twice within two years — the first time after the car crash that killed her husband. The second, well, those of you familiar with Heaven’s Gate will be able to guess what’s in store for those in Joseph’s orbit.

“Bright Objects” is not a rapid-fire page-turner or a wild freak-fest: It is instead a slow-burn meditation on grief, hope, mortality and what Joseph promises are “the laws of cosmic synchronicity.” Sylvia vacillates between quiet rage at the man she believes killed Christopher and an almost preternatural calm as she considers the world she is about to leave — while also trying to make room for her feelings for Theo, who provides her with the “opium of intimacy.”

There’s a soothing, near-mystical quality to the book’s language, a sense of being borne along on unseen currents, especially where Sylvia’s new lover is concerned. “I knew that should anything happen to break the motion of what our bodies were doing,” she thinks, “the atmosphere we’d entered would lose its blind logic, we’d question the terms of our surrender, and arrive in the room self-conscious and separate again.” What is on the page holds up a mirror to what is in the sky — luminous, unusual, unexpected.

And yet, when it comes to weighty prose, there can be too much of a good thing. Too often, Todd breaks the spell and stops the story. She describes rooms “holding themselves discreetly, as if attesting to the inherent rectitude of the lives lived there.” The comet pilgrims stand “with appurtenances of greater seriousness.” What’s more, Sylvia’s obsessive observation of every door, hand gesture and fleeting thought kills the vibe.

Still, a less daring and more conventional writer would have exploited and exaggerated the weirdness on display here. But Todd seems to understand that, at core, all cults and their leaders are the same — insecure, exploitative, duplicitous and a tiny bit boring.