In the future there is no disease, there is no natural death, there is no normal way for a human to die. Thats why there are scythes. Scythes are people that kill, if there is nothing that kills people, there needs to be people that will
Citra and Rowan are normal people, until they witness a gleaning, or the killing of someone by a scythe. These people were later introduced to the scythe that killed these people, and eventually became his aprentice, even thought they didn't want to.
After being an apprentice of this scythe, it was eventually their turn to glean someone. The scythe brought Citra and Rowan to her workplace, it was a shipping company. She was an old lady that was selected by the scythe for gleaning and she was very shocked that she was chosen. They watched at the scythe chose to kill her by placing something in her mouth in which when she bit it it would kill her. It was awful for them to watched but being an apprentice of a scythe meant that they would have to do that too