In the novel The Murder of Roger Ackroyd, Colonel Melrose is the Chief Constable of the county in which King's Abbot is situated. After the murder of Roger Ackroyd, because of the victim's prominence and because he knew the Ackroyd family personally, Melrose took a personal part in the investigation.
Melrose was at first unenthused to see the presence of Poirot in the case. However he warmed up when Poirot stated that he had retired and that he did not want his name mentioned and that he would help the police without taking any credit. From that point on, Melrose welcomed Poirot's presence. Above all, Melrose was concerned to solve the case quickly without having to bring in Scotland Yard. Poirot's help would be useful for that. For the same reason Melrose had brought in Inspector Raglan to supplement the local investigator Inspector Davis.