Your exam question asks you to focus on characterisation. The most important characters in “A Wasted Hour” by Jeffrey Archer are Kelley and John. Note that the narrator also mentions Kelley’s parents and several people whom she met while hitchhiking, but none of them play any significant role in the story.
Kelley is generally an observant person but, ironically, she does not recognise the man who claims to be John Steinbeck, the author of her favourite novel and a world-famous writer, whom she also studied in college.
John is not a developing character, as he does not change throughout the story. Note, however, that he does change in the eyes of the readers, who will be surprised by the ending if they do not know details about Steinbeck’s life.
Next, you can find both Kelley's and John's characterisation.