Final answer:
Christopher tells Siobhan that his murder mystery novel is finished because he has resolved the core conflict and provided a concluding arc for his characters, thus reaching the story's end.
Step-by-step explanation:
Christopher tells Siobhan that the murder mystery novel he is writing is finished because he has resolved the main conflict of the story, which involved the crucial struggle in the protagonist's life, and has made a conclusive decision regarding the future events. It is typical in literature that after a peak in the narrative arc such as overcoming 'evil passions' or 'a year of suffering', the story reaches a resolution where the fate of the characters is sealed, often leading to a feeling of finality and closure for both the characters and the reader.
In story writing, once all essential questions are answered and there's a sense of conclusion or catharsis for the main character, as represented by the end of their primary struggle, the narrative can be considered complete. This aligns with the examples mentioned, where character actions, following the climax of their respective journeys, indicate an ending, like the decision to lead a new and absorbing life, or the calm and implacable declaration of an ending as a prelude to a consequential action.