Plot
In the year 2042, effective immortality is discovered, and advanced medical technology allows most injuries to be quickly repaired. These revolutionary technologies allowed humanity to triumph over death and ended what is posthumously referred to as the Mortal Age. Earth becomes united under a nigh-omnipotent artificial intelligence called the Thunderhead, carefully designed with perfect motives. Utilizing all of humanity's knowledge and power, the Thunderhead solves climate change, mental illness, and discrimination. It also decides that death is still required in order to give life meaning, but is unwilling to be the means of death, as it is unable and does not want to be viewed as a killer.
Instead, a group of humans creates the Scythedom, an order of individuals who are responsible for killing ("gleaning") others permanently, unable to be revived by law. Scythes are entirely separate from the Thunderhead's rule, not having to abide by any law beyond the Scythedom's.
270 years after the Mortal Age, teenagers Citra Terranova and Rowan Damisch are informed by Scythe Faraday, that they have both been chosen to become his apprentices. They both live with Faraday as he trains them in various ways of killing. A few months later, Faraday takes his apprentices to the triennial regional conclave of Scythes, where Scythedom policies are discussed and various ceremonies are performed. At the conclave, Citra and Rowan are tested on knowledge. Citra is asked what her greatest wrongdoing was. Curie deems her to be lying. Rowan intentionally fails his question so that he remains with Citra.
Soon after the conclave, Citra and Rowan are informed that Faraday committed suicide in order to free them of their apprenticeship. However, this fails as Citra and Rowan are separated and taken on as other Scythes' apprentices. Citra is trained by Curie at Fallingwater, whilst Rowan is taken on by Scythe Goddard.
At the next conclave, the test requires Citra and Rowan to fight each other, and both fight with the intention of losing. Eventually, Rowan breaks Citra's neck violently. She is rushed out for revival and Rowan is disqualified. Once again they are tied for last.
Later, Citra is accused of murdering Faraday and she is hunted down, after which she temporarily kills herself. During her revival process, Curie brings her out of Chilargentine to Amazonia (formerly the top of South America) as a refugee. Citra discovers that Scythe Faraday is still alive and in hiding.
Meanwhile, Rowan's morals are put to the test as he experiences Goddard's extravagant lifestyle and harsh training. Goddard brings him on several mass gleanings, during which Rowan secretly helps people to escape. However, on one trip, during which Goddard takes Rowan to a cloister of a religious group of anti-Scythe cultists known as Tonists, Rowan kills Goddard and burns his body, preventing revival.
At the next conclave, the apprentices are given a final test. They must kill a family member. Although both Citra and Rowan pass, it is announced that Citra will become the newest Scythe. After choosing the name Anastasia, her first assignment is to glean Rowan. However, after she is given her Scythe's ring, she punches Rowan, transferring his blood to her Scythe's ring, granting him immunity for a year. He escapes the conclave and finds Faraday, whom Citra has waiting for him. They quickly drive away.
In the epilogue, Scythe Anastasia remarks on the recent stories of Scythe Lucifer, a rogue Scythe who hunts down corrupt and unworthy Scythes and permanently ends them. It appears that Rowan has become Scythe Lucifer. She states that she hopes that when they meet again, he will remember her as one of the good ones.
