Astarion Ancunín, an elven magistrate in the city of Baldur's Gate, lies dying in an alley after being beaten by street thugs. His skull is cracked, his arm broken, his lung punctured. A pale figure with red eyes appears and offers to save him for a price: immortality. The figure is a vampire, and Astarion accepts.
The narrative jumps forward nearly 200 years. Astarion is now a vampire spawn, an undead servant magically bound to Cazador Szarr, an ancient vampire lord who rules from the hidden Szarr Palace beneath Baldur's Gate. Spawn are immortal but wretched: forbidden from drinking the blood of intelligent beings, unable to defy their master, and denied the transformation into a true vampire that would grant autonomy. Astarion's role is to lure people back to the palace, where Cazador drains them.
Interwoven with the present-day story are flashbacks tracing Astarion's mortal life. He grows up on his father's vineyard in the rural Silver Marches, restless and bored. At age seven, a visit to the city of Silverymoon introduces him to silk and urban splendor. At twelve, a messenger named Bajia takes him to the manor of his great-grandmother, Lady Erikinia, an ancient elven noblewoman. Though his druid mother begs him to refuse, Astarion chooses to stay and is educated in deportment, speech, lock-picking, and knife fighting. His mother departs as a falcon. She returns when Astarion is thirteen, but he again chooses Lady Erikinia's household, and his mother leaves for good. At seventeen, he apprentices under his distant cousin Lazlo, a lawyer in Silverymoon, and falls in love with the law, recognizing it as a system of rules and loopholes perfectly suited to his mind. He also joins the local thieves' guild.
In the present, Astarion exists among five other spawn: Aurelia, the oldest, a tiefling with fiendish ancestry who taught him survival strategies; Dalyria, a former doctor who secretly believes vampirism is a curable disease; Petras, an arrogant human; Violet, a cruel and manipulative elf; and Yousen, a timid rock gnome. Cazador treats them as playthings, humiliating them and pitting them against one another. Astarion's one untainted pleasure is a secret collection of luxury fabrics, hidden in a concealed passage, which he touches in private to remind himself who he is.
When Dalyria asks Astarion to steal a vial of old unicorn blood from a defunct magic shop for her cure research, he agrees, partly out of boredom and partly to keep her indebted. The heist goes sideways when he accidentally triggers a magical singing harp and must flee from a shadow mastiff guarding the premises. He escapes with help from Rooftop Henry, an enchanted seagull-pigeon hybrid and member of the Thieves' Guild.
Cazador then announces a competition: Each spawn must fill an enchanted vial with the most exotic blood they can find, and the finest offering will earn the bearer true vampirism. Dalyria and Yousen ally with Astarion, revealing that an undead cult beneath the sewers worships a relic containing the living blood of the dead god Mask. Yousen, whose deep gnome heritage allows him to navigate underground passages, guides Astarion to a massive cavern guarded by soap mummies, corpses preserved through saponification.
Violet, who has been secretly following them, drops a thunderstone, a device that detonates with a thunderous blast, alerting the entire cavern. Astarion is captured and thrown into a cell with Hahn den Suriel, an aasimar—a mortal with celestial ancestry—and paladin of the Argent Badger, a minor knightly order that hunts undead. Den Suriel carries a faint divine glow. Astarion picks the cell locks and frees them both. As they fight through the tunnels, they pass a ward that blocks only the living, and den Suriel realizes Astarion is undead. The paladin's oath demands he destroy undead, but he has sworn to protect Astarion until their mission is complete. Astarion frames this contradiction as a legal loophole, and den Suriel reluctantly agrees to continue their alliance.
A flashback reveals the end of Astarion's mortal life. At twenty-seven, Lady Erikinia dies and names him her heir, burdening him with catastrophic debts. Lazlo gives him a false identity and sends him to Baldur's Gate. Bajia escorts him on the journey and, when an owlbear attacks, reveals herself to be a copper dragon who has lived in human form for years. Astarion feels betrayed by her deception. She leaves him on a bluff overlooking the city, and he walks toward it alone, vowing no one will take his new life from him.
In the present, Astarion recruits help from Lief, an enormous goliath and former pirate who owes him a favor. A druid polymorphs Astarion into a bat so he can fly undetected to the altar inside a sphere of magical darkness and fill his vials with the god's blood. The heist succeeds, but the undead priest raises the alarm. During the escape, den Suriel is impaled by a skeleton's spear. Astarion saves his life with a healing potion, holding the wound closed until it takes effect, and kisses him when his eyes open. Together they use a magical figurine that summons a living elephant to collapse a bridge onto the pursuing priest.
They shelter at the Rat's Run and sleep together. Afterward, while den Suriel rests, Astarion takes the blood vials and slips away, leaving a note: "I didn't want to be the one to break you."
On the waterfront, Violet ambushes him, shattering one vial with a crossbow bolt. The surviving vial falls toward the sea, but Rooftop Henry catches it. Back at the palace, Dalyria steals the vial and uses nearly all the blood for her experiments, leaving only three drops. Enraged, Astarion tells Dalyria her experiments will never succeed and reports her theft to Cazador, who sends her to be tortured.
During the tasting ceremony, Cazador samples each offering. He weeps when he tastes the three drops of Mask's blood, overwhelmed by the dying god's experience of losing its own existence. He calls it a gift but does not make anyone a true vampire, revealing the competition was another mind game. He tells Astarion that a full vial would have earned the transformation, a promise none of the spawn believe.
Den Suriel then storms one of Szarr Palace's entrances. Astarion convinces Cazador to let him handle the situation. Cazador orders that the door will open only when Astarion is dead, forcing the paladin to kill him to reach the vampire lord. Under a zone of truth, a spell that prevents those within it from lying, Astarion methodically dismantles every alternative den Suriel proposes. The paladin kisses him a final time, then chooses not to kill him. In that moment, den Suriel's divine glow extinguishes: He has broken his oath and become an oathbreaker. When Astarion suggests penance could restore him, den Suriel replies that penance only works "if you're sorry for what you've done." He leaves, diminished.
In the aftermath, Cazador carves a poem onto each spawn's back with a silver knife, branding them permanently. Astarion smuggles den Suriel's dressing gown into his secret hiding place alongside his silks and velvets. Over dragonchess, Aurelia reveals that a copper dragon was seen standing over Astarion's grave, suggesting Bajia remembered him. After drinking too much, Astarion embraces Aurelia and asks her to tell him this will end. She assures him that everything does, even immortal gods. The novel closes with Astarion resolving to endure until that day, while the blood of the dead god Mask drifts through the River Chionthar toward the sea.