There might also be an amateur detective, Mr. Thompson. He's a retired librarian who has a vast knowledge of history and uses it to solve mysteries that are often linked to historical events or artifacts.
There could be a detective like Inspector Brown. He's smart and observant, always on the lookout for the smallest details that can break a case wide open.
There could be a group of elves as main characters in one of the stories. They are working hard in Santa's workshop to prepare for Christmas. Their adventures and misadventures while making toys could be really interesting.
I'm not entirely sure without reading the book specifically, but typically in Saki's works, there are often characters from the upper - class society, like aristocrats or wealthy individuals.
Not having read 'the mystery man short story', it's hard to be definite. However, it's probable that the mystery man himself is a central character. There could be other characters like a local journalist who is intrigued by this strange man and tries to dig up information about him. Or perhaps a young person in the town who stumbles upon the mystery man and becomes involved in uncovering his secrets.
In many mystery kids stories, the main characters are often a group of friends. For example, in 'The Mystery of the Hidden Cave', the main characters are Tom, Jerry, and Lily. They are curious kids who are always looking for adventures. Another story might have a single main character like Tim in 'Tim and the Mysterious Key'. He is a brave boy who finds a key that unlocks a series of mysteries.
It's hard to say exactly without reading all the stories, but there could be a brave monster hunter as a main character in some stories. Maybe there are also some friendly monsters that help humans, and they could be main characters too.
In the 'book sherlock holmes short stories', Sherlock Holmes and Dr. Watson are the main characters. Holmes, with his sharp mind, is the detective we all admire. Watson, a reliable and intelligent man, is Holmes' partner. Additionally, there are other minor characters like Inspector Lestrade who sometimes seek Holmes' help and add to the complexity of the stories.
Perhaps a fearless adventurer is one of the main characters. This person travels from one city to another, facing different challenges and meeting various people along the way. They might be on a quest to find a lost relic or to solve a mystery that could save their world. Their courage and resourcefulness would make them a central figure in the short stories.
The main characters are of course the Dana girls themselves.
The main characters are of course Frank and Joe Hardy. They are brothers and amateur detectives. Frank is the older and more serious one, often thinking through problems carefully. Joe is more impulsive but also very brave.
Well, of course, Nancy Drew is the star. She's fearless and intelligent. Bess Marvin, who is one of Nancy's closest friends, is always there, even if she's a bit squeamish at times. George Fayne, Bess's cousin, is another main character. George is more adventurous and not afraid to get her hands dirty. And Carson Drew, Nancy's father, is a stable figure in her life, offering support and his own brand of wisdom from his legal profession.