During a raid on his camp, Richard is seriously wounded and now Nicci must use subtractive magic in order to save him. Richard awakens to find his wife Kahlan missing and discovers that he's the only person alive who remembers her. As he begins to search for her, he learns that he's additionally hunted by a beast created by Jagang's Sisters of the Dark.
Richard Rahl is the ruler of the D'Haran Empire, a collection of nations previously made up of D'Hara and the Midlands. Richard Rahl and the D'Haran Empire are currently locked in an epic struggle with the Imperial Order, an Empire from the Old World, led by Emperor Jagang.
Chainfire continues the storey of Richard in his attempt to teach the people that their lives are theirs alone, and that they can be free of the Imperial Order. Richard is gravely injured from an enemy's arrow. He is brought to Nicci, a sorceress and former Sister of the Dark, who heals him using subtractive magic; this causes unforeseen events to spiral out of control. When Richard awakens, he discovers that his wife, Kahlan Amnell, the Mother Confessor, is missing. Furthermore, no one around him seems to remember her. Nicci and Cara both attribute Richard's memory of Kahlan to dreams and delusions brought on by his injury and possibly an unintended effect of the subtractive magic used in healing Richard. Despite Richards attempts to explain the events of the last several years couldn't have happened without Kahlan, the paradoxes are explained away as Richard remembering things wrong.
Fearing for Kahlan's life, Richard desperately tries to find a few trace of her and at the same time convince the others that she exists. His search leads him to the witch woman, Shota, who reveals "that which you seek is long buried with the bones". In return for more information, Shota demands the Sword of Truth, which Richard relinquishes to her pet, Samuel, the previous bearer of the sword. Shota then utters the words "Chainfire" and "The Deep Nothing" and tells Richard to "beware the four-headed viper". She additionally warns Richard of a "blood beast" conjured by several wizards and Sisters of the Dark, under the orders of Jagang. The beast is meant to kill Richard and is as unstoppable as it is unpredictable. Further, the beast is able to track Richard when he uses his gift because of the way Nicci healed his arrow wound.
In the meantime, Ann and Nathan together have discovered a large number of blank pages in books of ancient prophecy. They seem to remember that the pages shouldn't be blank but can't remember what was originally written there. Zedd makes the same discovery independently.
Leaving Agaden Reach, Richard makes his way to the Wizard's Keep to find Zedd, but he additionally has no memory of Kahlan. Nicci arrives simultaneously. To prove Kahlan's existence, Richard exhumes her grave and is shocked to find a corpse in the buried casket with a nametag attached to her dress. He is devastated and falls into a deep depression. Meanwhile, Ann, Nathan, and Frederich additionally arrive at the Keep. Desperate to get their "Richard" back so that he'll 'fulfill prophecy' and lead the D'Haran army against the forces of Emperor Jagang, Zedd, Nathan, and Ann attempt to coerce Nicci into secretly using subtractive magic to delete Richards "delusions"; Nicci instead begs Richard to persevere in his beliefs. Together with Cara, they head to the Sliph to travel to the People's Palace.
Richard learns that the Sliph knows of a place called the Deep Nothing. The Sliph takes them to a few ruins called "Caska" in the Deep Nothing. Upon arriving, they find themselves in the midst of a group of Imperial Order advanced scouts who have captured a girl named Jillian, part of a people called the "Dream Casters". While Nicci eliminates the rest of the Imperial Troops scouts, Richard and Jillian look for answers in the catacombs. Together, they find a hidden passage that leads to a protected library. In the library, Jillian discovers a book titled Chainfire.
At the same time, the reader learns that Kahlan indeed exists, and has been kidnapped by the four remaining Sisters of the Dark who escaped the Dream Walker in Blood of the Fold. The Sisters have cast a spell called Chainfire, using subtractive magic to erase people's memories of Kahlan and Kahlan's memories of herself. The Sisters then use Kahlan to steal the boxes of Orden from the Garden of Life in the People's Palace. Kahlan leaves Spirit behind, the statue Richard carved for her.
Richard, Nicci, and Cara then travel to the People's Palace and learn that the boxes are missing and that they have been put into play. Richard finds the statue Kahlan left and figures out that the Sisters have stolen his wife and the boxes. With the proof in the Garden of Life, Nicci and Cara finally believe in the existence of Kahlan, notwithstanding not remembering her. While there, they learns that an older woman has been found fatally stabbed near the D'haran army; Nicci and Richard determine that it's Sister Tovi. Nicci uses deception to interrogate Tovi, discovering that it was Samuel who stabbed Tovi and took the Box of Orden she was carrying. She additionally learns about the Chainfire spell, about how it was used to obliterate everyone's memory about Kahlan, and that the Boxes of Orden were created in opposition to it. Later, Richard realises that the Sword of Truth protected him from the Chainfire spell, which is why he was still able to remember Kahlan.
Richard, Nicci and Cara return to the Wizard's Keep and, with the information gathered from Tovi and the book "Chainfire", they finally manage to convince Zedd, Nathan, and Ann of the truth. While no one but Richard remembers Kahlan, they now believe that she exists.
The spell is explained as a complicated memory altering magic. But it isn't as simple as erasing the memory of everyone directly, as this is merely Subtractive magic. Also, simply attempting to erase the memory because it uses Subtractive magic, has a strong probability of destroying portions of the mind, thus killing the subject. A death spell, can for instance, make it seem like a person is dead, but everyone still remembers the person existed. Also, if you tried to erase the knowledge of even a simple person like a woodcutter, the nature of reality would be such that all too obvious gaps in memory would be noticed, such as how the woodcutter's wife got her food and wood if she were crippled. For this reason, a few wizards came up with a workaround, using a few energy to warp reality itself or at least human perception of it. False memories are automatically created to fill the gaps in reality, almost as if someone went back in time and changed them.
Wizard's Ninth Rule
The Wizard's Ninth Rule, revealed in Chainfire, is:
A contradiction can't exist in reality. Not in part, nor in whole.— Chapter 48, p. 489, U.S. hardcover edition
It is explained in the novel as follows: "To believe in a contradiction is to abdicate your belief in the existence of the world around you and the nature of the things in it, to instead embrace any random impulse that strikes your fancy - to imagine something is real simply because you wish it were. A thing is what it is, it is itself. There can be no contradictions. In reality, contradictions can't exist. To believe in them you must abandon the most important thing you possess: your rational mind. The wager for such a bargain is your life. In such an exchange, you always lose what you have at stake."