The beginning of the novel takes place just after the events that ended The Infernal City. Prince Attrebus Mede was unaware of what caused his apparently fatal wound, cut from groin to breastbone and his guts spilled into his arms. The pain it caused he was well aware of, though, along with the sensation of being dragged by Sul, as well as the "stink of his bowels", a smell like rotting ginger, and the sound of Sul cursing in a language he didn't understand.
As he lay dying, he saw Annaïg Hoïnart, which motivated him to call out to Sul, who thought he was dead. In a fever dream, Attrebus saw a doll of himself that was ripped at the torso with the stuffing falling out. Huge hands pushed the stuffing back in along with something gray to fill the space that the stuffing couldn't, and sewed the doll up; he felt searing pain.
When he woke, he was in a room with a female with the pointed ears of an elf who introduced herself as Silhansa. She told him that she could hear a voice who claimed to be Malacath, and that this was his realm. He briefly explained the events that led him to his current situation. When Silhansa asked Attrebus about Malacath, he told her about the story his nurse Helna told him as a child. It told of Boethiah tricking Trinimac, eating him, and that the dung that came out afterward was Malacath.
In the conversation that followed, Silhansa transformed into a giant Malacath and held Attrebus in one hand and Sul in the other. Malacath had used the conversation with Attrebus to ensure that the curse of vengeance Sul swore was still with him. Due to what he described as a sort of love for curses and/or vengeance, Malacath agreed to help transport Attrebus and Sul to Solstheim to find the sword Umbra in order to stop Umbriel. He informed Attrebus that if he ever needed him, he'd let him know.
Mazgar gra Yagash was sent as a guard for the mage Brennus along with a group of other mages and soldiers to report on the state of Umbriel. The mages saw that it was moving toward Morrowind and that it was enclosed within a "bubble" of Oblivion. They realized when the army of dead attacked with Umbriel still eight miles away that the dead army need not remain close to Umbriel.
Colin Vineben was kidnapped from his bed and put on a boat. He wore a hood that was soaked in somniculous, which had caused unconsciousness at first, and his hands and feet were bound. After waking from the drug, he realized he was on a boat, and shortly they landed on shore. He heard the sounds of the two men who attacked him being killed, and recognized the voice of Letine Arese asking who he worked for. She explained that she was a double agent; a secret member of the Emperor's inner circle, and had also gained enough trust with Chief Minister Hierem to learn of his plans to have Prince Attrebus killed. She explained that Emperor Titus Mede wanted more information before he acted, and asked for Colin's help. He agreed.
Mere-Glim, in the Marrow Sump, smelled and retrieved the dying body of another skraw, Joacin. She, like all the skraws on Umbriel, was succumbing to the effects of the vapors they had to inhale to breathe underwater in the sump. He brought her now-dead body ashore, and his friend Wert and a younger skraw named Oluth discussed plans to demand something other than the vapors, something that didn't harm them. The maps he requested from them were ready, but he said it wasn't time to act yet. The other skraws expressed the growing sentiment that Glim was stalling. Glim took Oluth to show him how to harvest the Umbriellians that grew in the sump. Oluth revealed that he was a member of a group of younger skraws who called themselves Glimmers, who had pledged to help and follow him and talked of revolting against the Lords of Umbriel. Glim reiterated that he wasn't planning a revolt or fight, just a way to get them something that didn't kill them to do their jobs. While in the Sump, he was disturbed by the discovery of an Argonian growing.
Slyr entered the room Annaïg was in and apologized again for trying to kill her. Hovering, she was annoying Annaïg, so she asked her to sit while she explained the process of filtering chemical terror from a horse's brain through Chimera-Eel skin before passing soul energy through it to allow dishes to be seasoned with real terror. Slyr was wary of tasting the product but touched it, not knowing that it was also absorbed through the skin. She soiled herself in terror before Annaïg gave her an antidote in order to save her from going mad. After Slyr left, Chef Toel entered and expressed his disappointment that Annaïg allowed Slyr an antidote. He asked for a remorse seasoning, but Annaïg expressed doubt that it could be achieved using horse-brain. He says that a man named Kohnu was badly burned distilling phlogiston and his treatment would be time-intensive, so he would send his brain over. When Annaïg began to show reservations Toel rolled his eyes and said, "It's not as if you have to kill him yourself."
Glim and Annaïg met weekly in the old slurry filter. Annaïg explained that she was trying to figure out how the way the ingenium used souls was related to their inability to leave Umbriel. She expressed her feelings of guilt over the deaths of everyone in Qijne's kitchen and Kohnu, as well as the probable death of Attrebus. Glim explained his plans with the skraws, and expressed his feelings about the way they were forced to live. Annaïg was disturbed by the thought that the skraws might have been more important to Glim than stopping Umbriel.
Intendant Marall questioned Colin on his surprising find that the Thalmor were not connected to Umbriel. Colin stood his ground and suggested the An-Xileel, though he knew it was unlikely. Marall shared the intelligence that the undead army need not remain close to Umbriel, that it was in a "pocket" of Oblivion, that it was summoned, and that one of the undead armies was headed toward The Imperial City.
After Marall left, Colin discovered that the reports on the An-Xileel had been censored by Minister Hierem. He searched out Letine Arese and surprised her by approaching before she knew he was there. He confronted her with his discovery, and she explained that Hierem would have wanted to remove any trace of his visit to Black Marsh the previous year. Colin explained that recent reports regarding Umbriel had been altered. The one person he took with him, Delia Huerc, supposedly died of illness, and he would have paid for everything with his own money leaving no trace of his visit. Colin responded that though the explanation worked for the older reports, but that reports concerning the flying city had also been altered. After their discussion, she told him to come to her house if there was anything else to discuss.
In view of Tamriel's sun, Annaïg and Toel discussed his disappointment in her, and his desire to see her help his kitchen win a contest to determine which kitchen cooks for Umbriel. He explained that a rival kitchen, Phmer, developed an unknown ninth savor, and his could only win if they also had the ninth savor, more expertly prepared. Annaïg later told Slyr that she intended to steal the savor.
Annaïg sent a note to Glim via a skraw, requesting detailed information about Phmer's kitchen. He felt as though she thought her cause was more worthy than his, but he obliged, asking Wert for the information and at the same time finally allowing them to act by preventing some of the middens from draining to see if that would garner attention.
Glim, in the Fringe Gyre, was disturbed by the view below of walking corpses. Fhena approached, and Glim offered her a gift of Kraken barnacles. They discussed the trees in the Fringe Gyre, and discovered that they "spoke" to the people in much the same way the Hist spoke to the Argonians. Their sap can also alter things, as can the Hist's. Fhena placed Glim's hand on the bark of one of the trees, and the song he heard was familiar, like the one sung by the Hist, but "a little different- simpler."
Colin snuck into Delia Huerc's former home and was attacked by an otherworldly force. He retaliated first with a crystalline metal blade bound with consecrations, then with an inner power. After he defeated the attacker, he found Delia Huerc's ghost, who pointed toward her hidden journal when questioned about her trip to Black Marsh with Hierem. He left through an empty window when he heard steps in the hall, taking the journal with him.
Colin sat on the roof of a building that overlooked the alley behind Arese's house, eating and reading Huerc's journal. It revealed that Hierem performed some sort of ritual at the City Tree which involved the repeating of the name "Umbriel" many times. The last few lines of the journal lead to the conclusion that Huerc was voicing doubts about the Emperor's awareness of their expedition, and so Hierem poisoned her soup.
Arese not due home for a few more hours from her visit with her sister, he pondered what action to take, wondering if he could really trust her. As he waited, he saw a member of the Dark Brotherhood approach and then enter Arese's window. When he realized that Arese was inside the building, he sprung into action and leaped into the room, surprising and attacking the assassin. Though Colin was stabbed in the shoulder, he defeated the assassin only to discover another man coming at him, and him too worn to act quickly. Arese summoned a daedra, as she had obviously done in the house when he had been following her. The daedra made short work of the other attacker and was easily called off by Arese when it turned to Colin. The closeness they feel in the aftermath of the chaos quickly (stupidly, in Colin's thoughts) develops into an intimate moment despite the blood, sweat, and wounds.
As she later cleaned his wounds, they discussed the negative side of the life they led. She encouraged him to get out while he was young, but the thought of leaving her to that life alone angered him. He thought of the many men he'd witnessed her kill and the assassin he'd just killed, and realized that he felt nothing.
Fleeing to Cheydinhal from the armies of undead risen by Umbriel, Captain Falcus and the rest of the company- including Brennus, Mazgar, Merthun, Tosh, Coals, Glavius, Casion, Sugar-Lick, Kuur, and Na-Nasha- entered the village of Mountain Watch, speaking with the charter-holder Sariah. Falcus convinced the residents to flee along with them to Cheydinhal. Along the way, Brennus teased Mazgar about her pleasant demeanor with a young girl from the village named Lorcette but called "Goblin" for her ears.
Captain Falcar's company nearly made it Cheydinhal's gates before being attacked by the undead. Falcus ordered Mazgar to see Brennus to safety rather than join the battle. Goblin insisted Mazgar carry Riff Belancour, a boy with "a funny foot", instead of her. Closer to safety, she charged Brennus with seeing the children the rest of the way while she fought off a group of "wormies" in a rage, then followed after them.
The refugees set up a camp inside Cheydinhal's walls in order to eat and rest. The discussed the Morrowind-inspired architecture in the city, and then agreed to together climb the Chapel of Arkay to use Brennus tools and have a look outside the walls.
From the tower, Brennus and Mazgar saw that the undead army had stopped only a few hundred yards from the gates but out of range of their weaponry, which showed a level of intelligence not seen in the reanimated corpses common mages controlled. They also spotted Umbriel in the distance, advancing toward them.