In the novel The Murder of Roger Ackroyd, Miss Caroline Sheppard is the older, spinster sister of Dr James Sheppard. She has a notable gift of staying informed on all activities in King's Abbot. She is a friend of Colonel Carter and Miss Gannett. She does not catch sarcasm.
Despite being older than Doctor Sheppard, she considers her brother to be "quite an old fogey". Caroline was delighted when she found out that she lived near a famous investigator.
According to her brother, Caroline's incredible gift of knowing everything that happens in King's Abbot is due to her "secret service" which would consist of milkmen and parlourmaids.
She doesn't trust Inspector Davis, whom she believes is a "perfect fool".
Role in the novel (warning; may contain several spoilers)
Throughout the investigation of Roger Ackroyd's murder, Caroline tries to help Poirot and learn useful information to later spread around the village. She had told Poirot that he had heard Roger's stepson talk with someone about Roger's death in a suspicious way. Caroline's brother reproached her because she had just given Poirot a further piece of evidence that Ralph was guilty, but Caroline was surprised because she thought Dr Sheppard had already told that to Poirot.
The character of Caroline Sheppard was later acknowledged by Agatha Christie as a possible precursor to her famous detective Miss Marple. Caroline was a favourite character among many people and some believed she should have appeared in another novel.