It’s September of 1846. The expedition to find the Northwest Passage is officially underway with Captain Sir John Franklin commanding Erebus and Captain Francis Crozier commanding the Terror. Commander James Fitzjames serves under Franklin.

A young ship’s boy named David Young falls ill and hallucinates an Inuit man with the face of a bear. “It wants us to run!” he screams before dying. Dr. Henry Goodsir, Erebus’ assistant surgeon, cuts open David’s body to search for scurvy but finds none.

Erebus’ propeller becomes dislodged by a chunk of ice. Though the boat is compromised, Franklin still chooses to continue on it, despite Crozier’s warning not to. Soon, both ships become completely surrounded by pack ice.

Eight months later, both boats remain stuck in the ice. Sledge teams venture out to assess the conditions ahead, with Lt. Graham Gore leading a team south toward King William Land. While there, Gore’s camp hears an animal nearby and fires in its direction, accidentally shooting an Inuit man instead. A large bear attacks Gore, killing him.

Crozier keeps his distance from Franklin. Franklin wonders if it’s because Crozier wasn’t a top choice for the expedition – though he himself wasn’t either. He also remembers how Crozier was rejected by Sophia Cracroft, Franklin’s niece.

Gore’s team returns with the injured Inuit man and his daughter. It’s the same man from David Young’s hallucination. The daughter only speaks the Inuktitut language, which Crozier can speak as well. Goodsir is unable to save the Inuit man, leaving the Inuit woman to wonder how the “Tuunbaq” will obey her. Goodsir notices the Inuit man is missing a tongue.

The men speculate the connection between the Inuit family and Gore’s death. The Inuit woman remains mostly silent, earning her the nickname Lady Silence, but does warn the lieutenants they’ll disappear if they don’t leave. She goes back to her camp on the ice.
With no sign of the ice letting up, Crozier wants to send a rescue party South to the Hudson Bay Company outpost and have a team at the ready. Franklin dismisses his concerns.

Cornelius Hickey, Terror’s ship caulker, and Gibson, junior steward, enter a sexual relationship. It’s cut short when Lt. John Irving finds out. Gibson blames Hickey to protect his own standing with command and declares their affair off. Hickey tries to move up in rank as well.

Crozier pens a resignation letter, but must assume the role of captain when Franklin is killed by the bear. He proceeds with his rescue party plans and puts Lt. Fairholme at the helm. Hickey finds Crozier’s letter.

In London, Franklin’s wife worries about the expedition and starts rallying allies to form a rescue plan.

The bear attacks again – this time on the deck of Terror. The continued attacks rile up some of the men, particularly Hickey. They find Lady Silence’s camp and bring her back to the ships by force to interrogate her. Hickey receives 30 lashes on his bare buttocks as punishment for his role in her capture.

Crozier announces that Terror is sitting on a precarious pressure ridge and gives the men the choice to move to Erebus. Only ten men choose to stay on Terror.

Lady Silence is placed under Goodsir’s watch on Erebus. He extends kindness and begins learning her language. When she is moved to Terror, Goodsir decides to change ships as well.

The lieutenants learn more about the bear from Lady Silence. It’s called “Tuunbaq,” which translates to a Yupik word meaning “spirit that dresses as an animal.”

Crozier begins drinking heavily and missing command meetings. He eventually accepts he needs to recover and puts Fitzjames temporarily in charge.

The Tuunbaq strikes the Terror again. Ice Master Thomas Blanky is pursued by it and loses his leg in a chase. Lady Silence flees during the attack.

It’s January 1848. The Tuunbaq hasn’t been seen in months.

On the ice, Lady Silence asks the Tuunbaq to accept her as its new shaman. She cuts her tongue out as an offering, then makes her way back to the men.

Fitzjames throws a carnival party to uplift the crew’s spirits. Crozier cuts it short and admits they all must abandon both ships as soon as possible. He remains confident the Inuit people will help them on their journey.

Dr. Stephen Stanley, Erebus’ lead doctor, sets himself on fire during the party, causing the whole site to go up in flames. Terror’s lead doctor loses his life during the incident as well, leaving Dr. Goodsir as the sole medic.

Both ships are abandoned, though a small group of men voluntarily stay behind on Terror to wait for the ice to thaw and complete the Passage.

The men start their journey and set up a temporary camp, with Lady Silence among them. Dissatisfied with current circumstances, Hickey becomes interested in starting a “new arrangement.” He and a few others form their own group.

After discovering that some of their canned provisions are laced with lead, Goodsir urges Crozier to hunt for game. Though the men are falling ill from lead poisoning, Crozier insists they wait until they reach King William Island. Goodsir must keep it a secret, but Hickey notices when Goodsir stops Lady Silence from eating the food.

While on patrol, seven dismembered heads are discovered alongside an overturned boat. It’s Lieutenant Fairholme’s rescue party sent out a year ago, meaning there’s no help coming from the south. Crozier keeps it a secret when he finds out.

The men continue their journey and reach King William Island.

Crozier assembles two hunting parties to find game. Hickey and Farr make up one of the parties with Lieutenant John Irving leading them. During their escapade, Hickey kills both Farr and Irving and blames it on a Netsilik family. The camp arms themselves in case of a retaliation attack. Crozier sends Lady Silence away to protect her from the camp’s wrath.

When Crozier deduces that Hickey was behind the bogus attack, he orders him to be hung for his treachery. The entire camp stands before the gallows as Hickey offers his final words. Hickey reveals Crozier’s original plan to resign from the expedition and attempts to defame Crozier’s character. The Tuunbaq charges the camp, breathing in the souls of its victims. Hickey escapes amid the chaos. The mutineers grab weapons and supplies and run off on their own. They take a few others against their will, including Goodsir.

Crozier’s remaining men start walking south, running dangerously low on supplies.
Elsewhere on King William Island, the mutineers set up their own camp. When Hickey learns that Gibson’s health is deteriorating, he kills Gibson and forces Goodsir to cut up the body so the men can eat it.

Lady Silence talks with a Netsilik hunter about the competition for food on the island. The hunter plans for the Tuunbaq to “balance things again.” Lady Silence remains responsible to her people since the Tuunbaq is still hers.

After battling lead poisoning and trauma to previous wounds, Fitzjames grows terribly ill and asks Crozier to end his life. Crozier, having formed a deep bond with Fitzjames, obliges.

Blanky reveals a festering amputated leg and volunteers to sacrifice his life so Crozier’s men can journey on. He walks west to bait the creature and reaches a view of the shoreline where he sees three low islands in the distance. It’s the Northwest Passage. The creature finds him.

The next day, Robert Golding tells Crozier about a passageway he saw while out during a sweep party. It would save the men weeks of travel. Crozier scopes it out, but is taken hostage by the mutineers when Golding is revealed to be a mole.

While at the mutineers’ camp, Goodsir warns Crozier to only eat the soles of his feet should Goodsir’s body be made into a meal.

Crozier’s men vote to keep moving south as Crozier would have wanted. They leave behind those too sick to travel.

While alone, Goodsir rubs his entire body with a mixture of tinctures, drinks a bottle of liquid, then slashes his wrists with a shard of glass. After learning of Goodsir’s suicide, Hickey uses Goodsir’s body as food and forces Crozier to partake. Crozier eats the sole of Goodsir’s feet as instructed.

Crozier and a few of the mutineers are chained to a boat sledge and forced to pull it up a hill, where Hickey baits the Tuunbaq with gun shots. Hickey reveals he’s been impersonating someone so he could start a new life on the expedition.

The Tuunbaq appears and attack the men, while some vomit from eating Goodsir’s tainted body. Hickey cuts his tongue out as an offering and attempt to become the creature’s new shaman. The creature eats Hickey and immediately starts gagging from Hickey’s toxic soul. It slashes at Crozier, then collapses and dies.

Lady Silence finds the grotesque aftermath of the Tuunbaq attack and sees Crozier – the sole survivor – unconscious. She cuts his hand off to free him from his shackles and cares for him. When Crozier recovers from the attack, he and Lady Silence attempt to find Crozier’s men, but find nothing but corpses and evidence of cannibalism.

Lady Silence takes Crozier back to her village, where he’s welcome to stay during the winter. She leaves the camp as she can no longer be with the village since she lost the Tuunbaq, per their tradition.

In September of 1850, two years later, Sir James Ross has ventured out as part of a rescue mission. When he finds the Netsilik village, Crozier hides and instructs a hunter to tell Ross that Crozier is dead. The hunter passes along a warning from Crozier: “Tell those who come after us not to stay. The ships are gone. There’s no way through. No passage. Tell them we are gone. Dead and gone.”

Time passes and Crozier, now older, walks with the Netsilik across the vast landscape of ice. He finds a seal hole and waits in silence with a harpoon as a young boy sleeps peacefully beside him.