Novel Frankenstein is written in flashback method. The story in Frankenstein's dialogs and almost the whole novel is told in flashback. This way of telling a story is good because we have the impression that there are no mediums between the characters, it makes it a first hand story.
Flashback is a method that represents the disconnection of chronological order. When the story is told in flashback one continuous action is interrupted by the events that happened in the past. This way the writer gives us the background of the story and at the same time he continues with the story.
