Pushing Ice

Set in the mid-21st century, the novel opens with a prologue set 18,000 years in the future. Chromis Pasqueflower Bowerbird, a politician representing a cluster of worlds within a vast human civilization, travels to the Congress of the Lindblad Ring to propose a memorial project honoring "the Benefactor," a woman whose data transmissions from deep space accelerated human progress by millennia. The plan involves scattering billions of artefacts across the galaxy, each locked to the Benefactor's DNA. Chromis plays an ancient recording in which the Benefactor identifies herself as Bella Lind.

The story jumps to 2057. Bella Lind captains Rockhopper, a comet-mining ship operated by a company called DeepShaft. When Janus, one of Saturn's small moons, breaks orbit and accelerates toward the star Spica, 260 light-years away, DeepShaft orders Bella to pursue. She polls her crew of 145, and roughly 60% favor the mission. Ship's doctor Ryan Axford supports the chase because it offers the fastest route home for Jim Chisholm, Bella's terminally ill second-in-command. During the three-week chase, telescopic images reveal alien machinery beneath Janus's crumbling ice shell and an enormous structure near Spica, confirming the moon's alien origin. The builders are dubbed the Spicans. A rival Chinese vessel, the Shenzhou Five, commanded by Wang Zhanmin, races to intercept Janus but is apparently destroyed by a nuclear detonation after ignoring warning shots.

Svetlana Barseghian, Bella's chief of flight systems and closest friend, discovers that DeepShaft has secretly falsified fuel-tank data, making the ship appear to carry more fuel than it does. When headquarters claims Svetlana fabricated the evidence, Bella relieves her of duty. Svetlana lashes out, invoking Bella's past affair with Powell Cagan, DeepShaft's chief executive, and the confrontation severs their friendship. Near Janus, a mass-driver breaks loose and kills EVA worker Mike Takahashi, who becomes trapped in hardening sprayrock, a fast-setting repair material used in spacewalks. Axford performs the Frost Angel protocol, a contingency procedure that euthanizes and cryopreserves the body for possible future revival.

Shortly after, Svetlana diagnoses a worse problem: Rockhopper is caught in an invisible slipstream generated by Janus, accelerating at five gees without the crew feeling it. The ship is already traveling at nearly 5% of the speed of light. Escaping the slipstream would consume all remaining fuel, so Bella decides to stay near Janus, reasoning that its resources can sustain the crew. Craig Schrope, DeepShaft's company liaison, opposes her and recruits Svetlana, whose engineering expertise is indispensable. The crew splits. Svetlana begins a burn to escape, but Thom Crabtree, a crew member with neural implants that let him control robots remotely, threatens to ram the ship with a drone, forcing a reversal. In retaliation, two crew members murder Crabtree.

Svetlana assumes command. Accepting that escape is impossible, she sabotages the engine, lands Rockhopper on Janus's ice cap, and founds a settlement named Crabtree. Bella is exiled to an isolated dome. A fragment of the Shenzhou Five is found on the ice, and Wang, the sole survivor, is rescued with a forge vat, a nanotechnology fabrication device essential to the colony's survival. Over the following years, Svetlana's Interim Authority, the colony's provisional government, endures dwindling fuel, failing equipment, and factional tensions. Workers discover a rotating spire inside a vast underground chamber called the Maw and build a clockwork gear train to tap its energy, freeing the colony from dependence on fusion fuel.

In the twelfth year, enormous spires push through the ice and spread into a solid black ceiling called the Iron Sky, sealing off all view of the universe. Probes eventually reveal that Janus rests inside a tube-shaped segment of the Spica Structure. Schrope, who has slowly recovered from a years-long catatonic state, volunteers to enter a chandelier-shaped alien ship that lands on the Sky. Inside, he is crushed by rising gravity but glimpses the aliens before dying: enormous, blue, frond-covered beings the colonists name Fountainheads.

Bella then reveals a secret the dying Chisholm had entrusted to her: He wanted his frozen body delivered to any aliens they might encounter, hoping they could revive him. Svetlana carries Chisholm's cryopreserved body into the alien ship. The Fountainheads return him nine days later, cured of his tumor and wearing a spacesuit manufactured on Triton in 2134, evidence that the aliens have contacted a later era of humanity. Chisholm reports that the Fountainheads wish to trade access to Janus's energy for human technologies they have already acquired.

Thirty-five years after the Fountainheads' arrival, the colony has grown to nearly 500 people. Bella, rejuvenated by Fountainhead medicine, has been restored to power. She touches a mysterious memorial cube found orbiting Janus, and femtotech machinery, replicating devices operating far below the atomic scale, enters her body, projecting the personality of Chromis into her mind. Chromis reveals that the colonists have traveled far beyond Spica across tens of millions of years, and that the Structure is an ancient "zoo" built by the Spicans to gather samples of intelligent cultures from across deep time. Chromis also tells Bella that her husband Garrison, who died in a shuttle crash on Mars, had been clutching a lock of Bella's hair, proving he had forgiven her despite their last argument. This revelation releases Bella from decades of grief.

The Fountainhead diplomat McKinley warns Bella that Musk Dogs, a hostile alien species, are approaching through the Structure. Parry Boyce, the head of surface operations and Svetlana's partner, is sentenced to 50 years' imprisonment after confessing that he deleted evidence identifying three crew members who killed a colleague, choosing to protect the colony's workforce during its desperate early years. Enraged by Parry's sentence, Svetlana defies Bella and secretly visits the Musk Dog gristleship, a vessel of biological material wrapped around stolen alien technology. She trades Janus energy access for a door-opening passkey, but the Musk Dogs' true plan is to detonate Janus and breach the Structure's wall. Svetlana's attempt to fabricate the passkey causes a catastrophic femtotech rupture at the settlement of Eddytown, killing 93 of its 120 residents. Chromis sacrifices the memorial cube's mass to contain the disaster, destroying herself but extracting the completed passkey file.

Bella enters the ruins to rescue 27 survivors, including Svetlana's daughter Emily. On her return, she falls into a lethal gravity eddy and sustains a fatal skull injury. Svetlana retrieves her body, and the crew performs the Frost Angel procedure. Wang fabricates the passkey. As Janus convulses toward detonation, the colonists evacuate aboard the lander Star Crusader. Chisholm activates the passkey to close the Structure's endcap door, and a small frameshift drive, a faster-than-light device provided by the Fountainheads, allows the lander to outrun the Musk Dogs. Janus detonates behind the sealed door, destroying the Musk Dog ship.

Svetlana volunteers to take a rebuilt ship and 30 crew members through the breach in the Structure's wall to explore the external universe, accepting the mission as punishment for her role in the crisis. Before departing, she instructs McKinley to use neural patterns from her own brain to help reconstruct Bella's damaged mind.

Sixty-one years later, Bella awakens in New Crabtree, a settlement on the Structure's inner wall. Axford, now elderly, guides her recovery. She remembers fragments of the rescue but not her own heroic role. In the epilogue, Chromis learns her memorial proposal has narrowly failed. Undeterred, she resolves to try again, conceiving the idea of encoding the cubes with a copy of her own personality, determined to honor the Benefactor while her civilization endures.