I'm not entirely sure without reading it in detail, but there must be a detective or an investigator character who is trying to solve the mystery on the train.
Typically in such a mystery novel, there would be the passengers on the train. There could be a wealthy lady who might be the target of some plot. And, of course, there would be a smart and observant protagonist, perhaps a private detective, who starts to dig into the strange happenings on the train.
In 'the mystery of the blue train graphic novel', the main characters could include a resourceful investigator. This person would be intelligent and observant, constantly looking for clues on the train. Another character could be a friendly but naive young traveler who stumbles upon parts of the mystery. And there might be a shadowy figure lurking in the background, whose identity and motives are central to the mystery. There could also be supporting characters like other passengers, a train conductor, or a station master, each playing a role in the overall mystery.
The main plot involves a mystery that unfolds on the Blue Train. There's likely a crime or strange occurrence that the characters need to solve. It might involve the passengers on the train and their secrets.
There could be a variety of main characters in the 'big blue train story'. It might be a young adventurer who boards the big blue train to explore new places. Or perhaps an old, wise railway worker who has been taking care of the train for years. Also, there could be a group of friends traveling together on the train, and they all play important roles in the story.
Since there is no detail about this story, it's hard to tell. But in a typical train - related story, there could be a conductor as a main character. He or she might be responsible for the smooth running of the big blue train. There could also be a young adventurer among the passengers who has an exciting story of his own related to the train's journey.
I don't know for sure as I haven't read it. But typically in a mystery graphic novel, there could be a detective - someone smart and observant. Maybe there's also a sidekick who helps the detective in his or her investigations. There could also be a villain or someone who is trying to keep the mystery of the blue bottle hidden.
I'm not sure specifically as I haven't read it yet. But generally, it might be about a mystery that occurs on a blue train. It could involve characters like detectives or passengers, and the plot may revolve around strange happenings, disappearances or secrets on that train.
The central character is the girl on the train. She is a complex character with her own issues. Then there are the two people in the house she watches from the train, a man and a woman. Their actions and relationship are key elements in the plot as the girl on the train tries to piece together their story.
Since the title is 'the man on the train novel', the man on the train is the central character. However, other important characters could include an old lady on the train who tells him interesting stories about the places the train passes through. There could also be a young child whose innocent questions make the man reflect on his own life. And if there is a love interest involved, like a woman he meets on the train or is going to meet at his destination, she would be a main character as well.
The main character is Rachel, a woman with a drinking problem and a troubled past. There is also Megan, the woman Rachel spies on from the train. And Scott, Megan's husband.
The main character is the woman on the train. There's also the couple she observes from the train - the man and the woman in the house she watches. And there are likely some secondary characters like her ex - husband who are important in terms of her backstory.