In the novel The Mystery of the Blue Train, Miss Amelia Viner is a friend and confidant of Katherine Grey in the village of St. Mary Mead in Kent. She is two years older than Katherine's late employer Mrs Harfield, with whom she had gone to school.
Miss Viner was rather pleased that she had managed to outlive her younger friend, and attributes this to her habit of eating brown bread for supper every day. According to her, if Mrs Harfield had eaten a slice of brown bread every evening and taken a stimulant with her meals, she might have lived longer.
Katherine goes to see Miss Viner before departing for the Riviera. Miss Viner opines that although Katherine's "first freshness" had gone, she was sure she would find a man who would be interested in her.
Later, Miss Viner writes to Katherine at the Riviera to tell her that she has been diagnosed with cancer and has a year to live. Miss Viner writes that if Katherine had not inherited money from Mrs Harfield and gone off into grand society, she would have offered her double the salary to come and look after her. She tells Katherine that if things should go poorly, there will always be a home for her in St. Mary Mead. This makes Katherine homesick and gives her the desire to return to St. Mary Mead which, on reflection, is still home.
Miss Viner keeps a collection of newspaper cuttings, which she keeps in a box in a bureau drawer. Among these, she has a cutting about a robbery at Lady Tamplin's house, during which her jewels were stolen.
Miss Viner keeps her valuables, such as the key to the wine-cellar, and her jewellery, hidden in the stockings in the drawer of her dressing table. She considers this a more sensible place to keep her jewellery than her jewel case. She remembers that her father had had a safe put in, and her mother, Mary, would bring him her jewel case every night to be locked up. The jewel case was later stolen when burglars broke into the safe, but Mary had hidden her jewellery rolled up in a pair of corsets, not in the jewel case, and so it was still safe.
When Katherine asks Miss Viner if Major Knighton can come to visit, Miss Viner beings planning what food to serve him. She is of the opinion that "gentlemen like a nice piece of Stilton", and that no gentleman will be happy unless he has a drink with his meal. When Katherine tells her that it is not necessary to bring out the wine, Miss Viner tells her not to argue.
Miss Viner is at first suspicious of Major Knighton and believes he is only out for Katherine's money. When he arrives, she greets him with "dignity and an austere politeness", and only thaws after about ten minutes.
Miss Viner later retracts her opinion that Major Knighton is after Katherine's money. She explains to Katherine that when a man is truly in love, he cannot help looking like a sheep, and she had noticed that every time he looked at Katherine, he looked like a sheep.