The primary protagonist in Wizard's First Rule is Richard Cypher, a young woods guide. Richard lives in an area of the world known as Westland, which is one of three parts of the known world, divided by magical underworld boundaries. Of the three, Westland is united under one government and contains no magic, the Midlands are a coalition of sovereign nations with magic, and past another magical boundary lies the empire of D'Hara - a single kingdom ruled by Wizards. Richard works as a woods guide leading important political figures through dangerous forests, while his brother, Michael, is a newly elected minister of the Westland .
After the unexplained murder of his father, Richard feels compelled to investigate. He discovers a small piece of vine in his father's house, and searches the mountains for a live part of the plant, thinking it might lead him to the murderers. He finds the plant, but it attacks him, implanting a poisonous thorn. Trying to return to town to find healing help, he happens upon a woman named Kahlan Amnell, who is being hunted by a group of four men sent to assassinate her.
Richard helps to save Kahlan's life from the men, and learns that Kahlan crossed the boundary with the aid of five wizards searching for the First Wizard, who is rumored to have crossed into Westland after the creation of the boundaries. Richard takes Kahlan to his best friend and mentor, Zedd. Soon after arriving at Zedd's, Richard collapses from the illness caused by the vine after showing Zedd his vine piece. Zedd identifies the plant as snakevine, and treats Richard.
When Richard recovers from the snakevine bites, he identifies Zedd as the First Wizard who Kahlan seeks. Kahlan pleads for the help of Zedd, asking for him to name a Seeker of Truth who can confront Darken Rahl, the ruler of D'Hara who has activated the powerful magic "Boxes of Orden", which, depending how they are opened, could make Rahl ruler of the world, destroy all life in the world, or himself. Kahlan believes that the "Seeker" empowered by the Sword of Truth—an ancient magical weapon forged by the powerful wizards of old—can find a way to stop Rahl from gaining power or destroying life before the magic expires on the winter solstice.
Richard deduces a way to cross the boundary as a group, and with the help of a friend, the boundary warden Chase, Richard, Kahlan and Zedd travel south towards a pass in the boundary. They encounter underworldly creatures, hearthounds which are escaping the weakening boundary, and Chase explains that their escape signals the fall of the boundary—similar to a fall in the boundary between the Midlands and D'Hara. During one of the encounters, both Chase and Zedd are dangeously injured, but Kahlan and Richard manage to find the pass. In the pass, they meet the mysterious bone woman Adie, who gives shelter to their injured companions and teaches them how to go through the pass.
Kahlan and Richard journey through the pass, nearly getting killed by the dangerous creatures that live in between the underworld of the boundary and the world of the living. Once through, Richard asks Kahlan to lead them to the village of the Mud People, a tribe that has the ability to contact spirit ancestors for guidance on how to prevent Rahl from seizing the third box of Orden.
To summon the ancestors, after the tribe requires them to be members of the tribe. During this time, a Richard and Kahlan find they love each other more and more, but a secret power held by Kahlan prevents a full and honest relationship. After convincing the Mud people that Richard and Kahlan are honorable, and seek to help all humans, including the Mud people, they become members of tribe. Once members, the elders summon mud people's ancestors, and they learn that the witch woman Shota, one of the most feared people in all the Midlands, can reveal the location of the last box of Orden. While in the gathering Darken Rahl slaughters several mud people and kidnaps Siddin, the son of an elder and friend of Richard.
Richard and Kahlan travel to Shota's territory, Agaden Reach where they learn that Queen Milena has the last box. Kahlan finally tells Richard, her secret, that she is a Confessor, an enchanted person whose power of love destroy the minds of others by making them absolute slaves to her will. Shota also warns Richard that both Kahlan and Zedd will use their powers against him. From Agaden Reach, they travel to Tamarang, seat of Queen Milena, meeting back up with Zedd along the way. Upon reaching Tamarang, they discover that the last box is gone and eventually realize it was given by a former pupil of Zedd's, Giller, to a small girl named Rachel for safekeeping.
Soon an artist who can control enchantments, separates Richard from the group and he falls into the hands of a Mord-Sith named Denna who brutally tortures him for a month. The Mord Sith report to Darken Rahl, and Rahl hopes to force Richard to recite the Book of Counted Shadows, a magical book which Richard had memorized under the bequest of his father. However, Richards innate gentleness alters their relationship, and Richard eventually breaks free of Dennas control by turning the Sword of Truth white, with the power of love for her, rather than the sword's typical harness of anger. Rahl allows Richard to wander free, but sets a wizard web on him which makes all of his friends think Richard is an enemy,
After helping a dragon named Scarlet find her egg which had been kidnapped by Rahl, Richard discovers how to both beat Rahl, and be with Kahlan. Kahlan, falsely thinking Richard dead by Rahl, enters the Con-Dar, or a powerful Blood Rage. Thinking Richard is in fact Rahl, she uses her powers on him. Rahl, thinking Richard is now at his mercy, uses him to recite the Book of Counted Shadows. In the end, Rahl opens the wrong Box of Orden, under Richard's false guidance, thus killing Rahl. Kahlan, alone by a pool, orders Richard to leave, thinking he is still under her power, and Richard reveals he was protected, by his already complete and unconditional love for her.
The reader learns at the end of the novel that Richard is the progeny of Rahl's rape of Zedd's daughter. Thus, Zedd is Richard's grandfather, and Richard is the new Lord Rahl. Relieved at their victory, Kahlan and Richard set off for the Mud People's village to return Siddin to his parents.
Each of the novels in the Sword of Truth series reveals a "Wizard's Rule"—a magical principle that allows Wizards to be savvy manipulators of the world around them. The novel reveals the Wizard's First Rule:
"Wizard's First Rule: people are stupid." Richard and Kahlan frowned even more. "People are stupid; given proper motivation, almost anyone will believe almost anything. Because people are stupid, they will believe a lie because they want to believe it's true, or because they are afraid it might be true. People's heads are full of knowledge, facts, and beliefs, and most of it is false, yet they think it all true. People are stupid; they can only rarely tell the difference between a lie and the truth, and yet they are confident they can, and so are all the easier to fool.""Because of Wizards First Rule, the old wizards created Confessors, and Seekers, as a means of helping find the truth, when the truth is important enough. Darken Rahl knows the Wizard's Rules. He is using the first one. People need an enemy to feel a sense of purpose. It's easy to lead people when they have a sense of purpose. Sense of purpose is more important by far than the truth. In fact, truth has no bearing in this. Darken Rahl is providing them with an enemy, other than himself, a sense of purpose. People are stupid; they want to believe, so they do."
— Chapter 36, p.560, U.S. paperback edition