Final answer:
In detective fiction, investigators are not always professional detectives by trade. Examples include characters like Sherlock Holmes and Miss Marple.
Step-by-step explanation:
In detective fiction, investigators are not always professional detectives by trade. In many detective stories, the main character may be a police officer or a private detective, but there are also instances where the investigator is a regular individual with no professional training in the field of investigation.
One example of this is the character of Sherlock Holmes, created by Arthur Conan Doyle. Although Holmes is often portrayed as a consulting detective and a master of observation and deduction, he is not a police detective by profession. Instead, he is a private detective who uses his unique skills to solve crimes.
Another example is Miss Marple, a character created by Agatha Christie. Miss Marple is an amateur detective who solves crimes in her village using her knowledge of human nature and keen observation skills.