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Faced with an invasion of monsters, the nation of Inath attempts to summon a Hero, and instead gets Morey, a regular citizen of 21st century Earth. Nonetheless, the Queen gives Morey a team of mages and sends him to search for the Legendary Sword.
Meanwhile, in an unexpected side effect of the summoning ritual, an engineer from Earth named Cato finds himself in the backwoods, far away from Inath's capital. Cato meets a village of part-human Fukas and Elkas, who help him to get his bearings, and he helps them to fend off monster attacks by identifying and targeting the monsters' weaknesses. However, when the attacks escalate to hordes of zombies, he persuades them to leave and seek refuge with a human-built fort.
At the fort, Cato meets Landar, the "Mad Alchemist" and runaway daughter of the powerful Iris clans, who is prone to brilliant ideas that aren't always workable. Together, they develop the "bowgun", a magically assisted arrow launcher, which gets the attention of the fort commander. However, there are racial tensions, and after it becomes clear that the Fukas have used the bowgun to arm themselves, the commander becomes annoyed and asks Cato to leave.
Cato and Landar, along with Fuka stowaway Danine, establish themselves in the town of Corbin, where Cato introduces a food merchant, Kalny, to the Bessemer process for making steel. However, the project is fraught with difficulties, and the resulting furnace is sabotaged by the Ironworkers Guild, who also copy the plans. Kalny comes out ahead, though, when Cato introduces him to the idea of pasteurizing food to preserve it, opening up a whole new field of business for him. Cato and Landar also reach out to establish a waterwheel-driven paper mill, and introduce a builder, Muller, to the idea of bricks with iron cores. The Ironworkers continue to study the furnace, too, resulting in the spread of knowledge, albeit not quite how Cato intended.
The mayors of Corbin and nearby Selabia become interested in Cato's work, and offer him a steady job working for them. However, they are largely interested in improving the bowgun, to build up a militia and improve their political standing, brushing aside Cato's desire to spread technology widely and focus on civilian applications like improved farming. When he refuses their offer, they attempt to imprison him by force, but Landar helps him escape, and they turn to the mayors' superior, Chancellor Minmay. Danine remains behind to help organize the Fukas of Corbin for protection against racially motivated gang attacks.
Around the same time, Morey and the party of mages assigned to him discover that large groups of zombies are developing new abilities, including a magical shielding aura and siege-level laser beams. Morey is able to hold them off by adapting spells to penetrate the shield aura, and reorganizing the knights to use their skills in coordinated and complementary ways instead of over-specializing and fighting haphazardly as individuals, but the threat is not gone.
The chancellor embraces Cato's ideas, spreading double plows and seed drills all over the region and teaching peasants to access their magic so that it can be tapped for industrial use. Cato also establishes a university in the capital city, to research and test new ideas and freely spread them; it quickly gathers widespread interest, with people starting to investigate possibilities from umbrellas to improved cement to hot air balloons.
The first wave of technology starts to encounter problems when a famous assassin is sent to the university, aiming to capture Cato and kill anyone protecting him, and spies are sent to steal books that Cato has written. At the same time, the greatly improved harvests result in social upheaval, with large numbers of peasants becoming unemployed and moving to the city. However, the assassin is caught in a trap, and Cato deliberately leaks copies of his books, including designs for a printing press so that they can spread faster.
Morey meanwhile triggers a revolution in the country of Illastein, when he encounters their system of chattel slavery. His party are divided, some helping him and others protecting the government, but they eventually unite behind him for pragmatic reasons when they see the momentum he's gathered through propaganda (including the new printing press) and guerrilla tactics, preferring a quick victory to a messier one with the possible loss of the Hero.
With steel production greatly increased and still expanding, Minmay establishes a peacekeeping force, armed initially with crossbows. However, with Cato's encouragement, Landar has been devising standardized enchantments and signaling that allow her to create a cannon capable of firing spells from crystals of stored magical power, rather than direct input from a mage. Armed with spell cannons, the Minmay Guards are able to defeat an invasion by jealous neighbor Duport. They also use them to launch ice spells for fire suppression when a large fire breaks out in the capital city; however, the large heat source attracts natural magic that forms a firestorm in the sky, inflicting widespread damage. Cato advises Minmay to take the opportunity to restructure the city, properly tracking construction and using property taxes to pay for standardized services (water, sewerage, peacekeeping, etc).
Based on the way that the firestorm gathered magic, Cato and Landar discover that magic also accumulates in the ground, launching a new era of magical power by drilling boreholes to pump it out. Landar also devises "magic circle" enchantment systems that allow the construction of magic items without needing a human trained to shape the magic directly. Cato focuses on standardizing manufacturing procedures so that carpentry and ironworking and similar procedures can be performed with detailed instructions and effective tools instead of years of training, allowing industry to take in the influx of out-of-work farmers; all kinds of manufacturing undergo huge growth as a result.
The two of them also visit Landar's family, the Iris clans, during negotiations between Minmay and King Ektal. Having seen how well Cato and Landar get along (a novel situation for Landar), her father is hopeful that they will marry, but Landar resents her father's involvement and duels him, scraping a win by using Cato's research into the nature and weaknesses of magical shields. Cato and her mother, however, try to persuade her that her father does have her best interests at heart, as he sees them.
Unfortunately, the guilds are unhappy about being displaced by novices, and some of them collaborate with disgruntled neighbours like Mayor Corbin to stir up popular discontent. Chancellor Minmay learns about the plot early enough that he is able to pre-empt it and force a confrontation before the rebels are prepared, but there is a heavy death toll, as the Guards slaughter angry peasants, and Cato is upset. Nonetheless, Minmay insists that it was necessary to clean house, and establishes a clear legal code in the aftermath, as well as abolishing local mayors and centralizing the government.
Morey's uprising in Illastein meanwhile gains enough momentum to take control of a significant part of the country, despite an unfortunate amount of brutality on both sides. Morey himself does attempt to keep the rebellion as civilized as possible, but is not able to completely prevent the use of suicide bombers, child soldiers, and gleeful public executions. He reaches out to Queen Amarante and is able to arrange for her to send advisors to help stabilize the country in the aftermath, so as to prevent a power vacuum and collapse.
Minmay's actions, gathering an army and absorbing other rulers, put strain on his relationship with King Ektal, which leads Queen Amarante to mediate; she brokers an agreement that they will both send the majority of their forces north to fight the ongoing zombie threat. Minmay uses it as an opportunity to form a "special effects" team for testing experimental weapons, to great effect against large zombie armies, although it relies heavily on consumable items and requires a strong logistics chain. The discovery of oil leads to the creation of napalm-like "liquid fire", and Landar also develops workable, albeit inaccurate, rocket artillery.
Morey resumes his search for the Sword, and finds a time capsule from the ancient civilization known as "the First". The message warns that the ancient war between the First and the Tsarians included interference from an unknown but hostile third party, which sabotaged their tools and weapons to destroy them all and end magic; the presence of magic now suggests that the world has healed, but there is a risk that the enemy might still exist. Morey hopes to also find a path back to Earth, but to no avail.
After extensive discussion and consideration, Cato and Landar become engaged to be married. Her parents support the match, especially since research sponsored by Cato has resulted in a more efficient magical training regimen that has catapulted her father to head of the Clans, but some other Clan leaders are skeptical about Cato's fitness to marry an Iris when he himself cannot use magic.
Scouting missions by Elkas reveal that there are zombie-infested cities to the north, and the Inath federation, including both Minmay and Ektal, agree to go on the offensive and try to break the zombies' power for good. At the suggestion of Landar's father, Cato joins the expedition so as to have more visible achievements that can convince the Iris to accept him.
Despite initial difficulties with a new type of zombie monster, the expedition succeeds in clearing the first city found by the Elkas and establishing a base there. The Elkas then make contact with another nation living in the north, which is holding off zombie onslaughts through a combination of dogged persistence and a magic system powered by human sacrifices.
