Plot
Set in a world where mercenary groups (or "bands") are akin to rock stars and rock bands, Clay "Slowhand" Cooper (nicknamed as such due to commonly getting hit first in every fight) lives a quiet life in Coverdale as a watchman with his wife, Ginny, and his young daughter Tally (short for Talia). One day he finds his former bandmate and best friend Gabriel on his doorstep, and Gabriel tells him he came to get Clay's help in getting their former band, Saga, back together in order to rescue Gabe's daughter Rose, who joined a band and is now trapped in Castia, a faraway city surrounded by monsters and about to be besieged. While Clay initially refuses to accompany Gabriel, Tally convinces him to go.
After setting out, Clay visits his mother's grave, and he and Gabriel both get robbed by a group of bandits led by the affable Lady Jain, who allows them to keep Clay's shield, Blackheart. They arrive in the Free City of Canthas and meet up with Kallorek, their old booker, who has since expanded his operations. Kallorek is in possession of Vellichor, Gabe's fabled artifact sword, but refuses to relinquish it and pursues Clay and Gabriel when they go to get Arcandius Moog, Saga's main mage. They use Moog's portal mirror to escape and end up in the palace bedchamber, where they find Matrick Skulldrummer, the Band's former rogue and now king. They attend the Company of Kings, a gathering of monarchs from across the country, and encounter Lastleaf, the druin son of Vespian, Master of the Heartwyld Horde about to besiege Castia, and Saga's archenemy. The assembled monarchs attempt to get Lastleaf to disband the horde, but Lastleaf refuses and instead tells them not to interfere. Matrick's wife Lilith doesn't want Matrick to leave the palace, fearing he will sire a true royal heir, so the Band fakes Matrick's death to continue their journey.
After encountering Lady Jain and her bandits again, who cook breakfast for them before robbing them again, Gabriel uses Moog's crystal ball to see Castia and becomes discouraged after seeing the sheer size of the Heartwyld Horde. Clay gives him words of encouragement, and they progress to Fivecourt, where Gabriel retrieves a sack of gold to bargain with Dinatra (a Gorgon noblewoman) for Ganelon, the final member of Saga, who has been petrified for nineteen years as punishment for murdering the Sultana's son and, as such, has not aged as much as the other bandmembers. As payment for freeing Ganelon, Saga is forced to fight a Chimera in an arena, and the Chimera manages to incapacitate everyone except Ganelon, who manages to kill it. The arena is destroyed in the battle, and Saga is rescued by Vanguard, another band who are old friends of theirs.
Saga decides to raid Kallorek's collection of magic items, and Gabriel takes back Vellichor, while Clay takes the Warskin (an impenetrable suit of armor) and a frigid sledgehammer he names Wraith, while Moog gets a magic food-producing wizard's hat and Matrick takes an insect-firing horn. The Band gears up, takes Kallorek hostage, and commandeers his flying ship, where they meet Kit, a posh and friendly revenant poet and storyteller previously imprisoned by Kallorek and accidentally freed by the Band, who joins Saga as their bard. Before departing, Gabriel, Moog, and Kit set out to gather supplies, while Clay and Ganelon were tasked with gathering any new information about Castia. They enter a bar where they encounter Lady Jain and her bandits again, who have now reformed and are now a band. They are cornered by Larkspur, a daeva bounty hunter hired by Lilith to find and return Matrick, and manage to escape from her with Moog's help.
They take off in their skyship and have a relatively uneventful few days. Clay throws Kallorek off the ship after Kallorek threatens Ginny and Tally, and not long after they enter the sky above the Heartwyld, a monster-infested forest filled with nightmarish creatures, deadly plants, and the Rot (an incurable wasting disease). They are ambushed by Larkspur in her own skyship, and in the ensuing fight, Larkspur manages to fly off with Matrick but is struck by lightning and plummets to the forest floor. Saga sets down to search for Matrick, and while searching, Ganelon reveals to Clay that he was fully conscious for the nineteen years he was petrified, to Clay's shock and horror. They find Matrick being tended to by a friendly witch doctor troll named Taino, as well as an amnesiac Larkspur, who displays a whole new personality named Sabbatha and has broken one of her wings. They decide to take Larkspur/Sabbatha with them and are attacked by a cannibal tribe. Ganelon kills their champion by crushing him under a tree, and the tribe makes peace. Moog discovers that the Rot can in fact be cured by Mudweed, much to his excitement and grief (Moog lost his husband Fredrick years earlier and has been grieving since). Moog leaves his magic food hat with the cannibals, and the Band also recruits Dane and Gregor, an ettin.
Saga's skyship is destroyed by Larkspur's monk thralls, so the Band treks through the Heartwyld, eventually setting camp in the ruins of a fort. They meet Shadow, another druin and a wandering trader, and Shadow tells them the story of Vespian and Lastleaf. Vespian was the ruler of the Dominion, the druin's mighty empire, and after his wife Astra died giving birth to a daughter, Vespian went mad with grief and made a sword, the Tamarat, which, upon killing a druin, would resurrect Astra. Vespian sacrificed his daughter, and Astra killed herself from grief, so Vespian sacrificed countless druins to resurrect her over and over again. Eventually, Astra gave birth to Vail, a son, who stole Tamarat from his father to break his mother's cycle of horrible rebirth. Vail eventually became Lastleaf and has spent years making deals with monsters, culminating in the Heartwyld Horde.
Moog realizes Shadow is aligned with Lastleaf, and Shadow states he wants to take back Vellichor, the sword Vespian gifted to Gabe, for Lastleaf. He distracts the bandmembers with ghostly clones of themselves but is eventually decapitated by Larkspur with his own scythe, which she takes for herself. The Band continues trekking to Castia, encountering a (previously thought to be fictional) Owlbear that they are forced to kill and adopt the twin Owlbear cubs. They debate on which path to take through the mountains, and the decision falls to Clay, who elects to take the Cold Road, a treacherous and deadly but quick pathway. Sheltering in a cave, Ganelon and Sabbatha play Tetrea (similar to Chess), while Kit shares how he died: he was executed by the Emperor of Castia for killing his phoenix while drunk long ago. Ganelon and Larkspur then sleep together.
While crossing the last stretch of the Cold Road, they are attacked by Rasks, and Gregor is killed when one slashes his throat. Sabbatha turns on the Band, revealing that she was faking her amnesia and her broken wing the whole time, and takes Matrick after cutting off Clay's hand. Clay falls down a ravine but survives, finds Dane still alive, and keeps him company in his final moments. Clay finds Matrick, who has given up hope, and is discovered and assaulted by Larkspur and her followers before Matrick, revitalized, steps in. They are both saved by Vanguard again, and Clay is healed and has his hand regrown, while Matrick gives up alcohol. They reunite with the rest of Saga and devise a plan to steal the key to a nearby portal from the dragon Akatung. Matrick is sent to steal the keystone, and they manage to evade Akatung long enough for Moog to use the portal to send the dragon to the bottom of the ocean. They then open the portal to Kaladar, in the middle of the War Fair, the biggest gathering of mercenaries. Gabriel riles the mercs and leads his new army to fight the Heartwyld Horde, and Gabriel duels Lastleaf while Clay is sidetracked by a Minotaur. Larkspur arrives, having had a change of heart, and kills two giants. Gabriel defeats Lastleaf, who flees, and the mercenaries manage to defeat the Horde. Gabriel reunites with Rose, while Clay discovers that Lastleaf stabbed himself with Tamarat, thus resurrecting Astra, the Winter Queen.
Matrick becomes the new emperor of Castia, and all of his illegitimate children choose to stay with him. Moog makes the cure for the Rot publicly available, and Ganelon chooses to go back to the Quarry, waiting for Larkspur (whom he unknowingly left with his child). Clay heads back to Coverdale and reunites with his wife and daughter.
