In the year 2147 of the Chrona Era, the fractured realm of Chrona balances on the edge of annihilation. Floating continents tethered by clockwork bridges loom over the Hourglass Wastes, a desert where dunes flow backward, burying relics of erased futures. Here, exiled horologist Arin Vey scavenges for time crystals—shards of solidified chronology—until a dying engineer stumbles into his camp, clutching a gear etched with coordinates to the Celestial Gearspire's core. With his final breath, the man whispers, "The Cog is a lie." Arin deciphers the warning: the Gearspire, a colossal structure stabilizing all timelines, is not a marvel of engineering but a prison. And in seven days, during the Convergence—a cosmic alignment of temporal energies—the Chronos Collective will collapse it to free a primordial entity.

To prevent reality's unraveling, Arin assembles a crew of outcasts: Zara Kael, a rogue pyrokinetic engineer whose cybernetic arm channels unstable chronal energy; Taryn Voss, a disillusioned Collective enforcer haunted by fragmented memories of her role in a sentient automaton's destruction; Corwin Slate, the automaton himself, housing the consciousness of Arin's mother; and Lyra Solène, Zara's estranged sister, a smuggler trading in stolen minutes. Together, they infiltrate the Gearspire, navigating labyrinthine corridors where gravity shifts hourly and echoforms—ghosts of erased possibilities—stalk their every move. But the Collective's leader, Kael Thorne, awaits. A man obsessed with resurrecting his wife, trapped in an endless loop within the entity, Kael will sacrifice the Spire—and all existence—to reclaim her.

As the crew battles echoforms of their past selves and uncovers Seraphine Vey's buried legacy, Arin learns the horrifying truth: the entity feeds on erased timelines, and only a Chronic—someone born with time-sensitive blood—can contain it. But containment demands sacrifice. Seraphine's spectral form guides him, urging him to merge with the entity, though it will erase his existence. Zara's fire crystal, holding her consciousness in a recursive prison, flickers with defiance. Taryn grapples with her implant's revelations: she was engineered to kill Arin if he falters. And Corwin, slowly dying as his molten silver core leaks, whispers of the entity's whispers: "You cannot escape what you are."

The Convergence peaks. Arin stands at the Prime Cog, Kael's echoform fused with the entity, Zara's crystal shattered, and Taryn's loyalty torn. The Spire disintegrates, timelines fracturing. In his final moments, Arin faces an impossible choice: reset the Spire, erasing his crew's memories and damning himself to obscurity, or merge with the entity, preserving reality at the cost of his soul. But Zara's crystal shatters anew, revealing she has hosted the entity's consciousness all along. The novel closes with Arin's hand hovering over the Cog, timelines splintering, his decision unmade—and the entity's laughter echoing across the void.