Well, the traits of a mystery novel include a complex plot. There are often multiple layers of events and sub - plots that are all related to the main mystery. Also, red herrings are common. These are false clues that mislead the reader and the characters in the story. And the setting can be very important, sometimes a spooky old mansion or a dark alley which adds to the overall atmosphere of mystery.
A mystery novel typically has the trait of a strong sense of intrigue. The author creates questions in the reader's mind right from the start. There is also the use of foreshadowing. Little hints are dropped throughout the story that might seem insignificant at first but later turn out to be crucial in solving the mystery. Moreover, the characters often have secrets. Each character may be hiding something that is related to the overall mystery, which makes the readers eager to dig deeper into their personalities and motives.