The length of a mystery novel depended on the complexity of the plot and the speed at which the plot progressed. Generally speaking, the plot of a mystery novel should have enough depth and complexity to allow the reader to think and explore the story. At the same time, the plot should have enough speed and reversal to keep the reader nervous during the climax of the story. In order to write a long suspense novel, you can consider the following points: Increase the depth and complexity of the plot: The plot of a suspense novel should have enough depth and complexity to allow the reader to think and explore the story. You can increase the depth and complexity of the plot by adding background stories, contradictions, and motives to the character. 2. Excavate the details of the story: The story of suspense novels often has a certain degree of concealment. By excavating the details of the story, the authenticity and legibility of the story can be increased. You can add details to the story by describing the habits, speech, and behavior of the characters. 3. Increase plot twists and turns: The plot of a suspense novel should have enough speed and twists to keep the reader nervous during the climax of the story. The story could be made more readable and tense by adding twists and turns to the plot. 4. Maintain the continuity of the story: The story of a suspense novel should be coherent to avoid the abrupt and unreasonable plot. Through appropriate dialogue and description, the story's cohesiveness and rationality could be enhanced. 5. Increase the background and setting of the story: The story of suspense novels often has a certain background and setting. By increasing the background and setting of the story, the depth and complexity of the story can be increased. To write a long suspense novel, one needed to pay attention to the complexity of the plot, the excavation of details, the speed of reversal and advancement, the cohesiveness of the story, and the setting of the background.