In the novel After the Funeral, Mr Entwhistle was a partner of the law firm of Bollard, Entwhistle, Entwhistle and Bollard. He was a personal friend of Richard Abernethie and the Abernethie family solicitor. After Richard's death and funeral, he read out Richard's will to the family. When Cora Lansquenet mentioned that Richard might have been murdered, and is herself murdered the next day, Entwhistle linked the two events. After speaking to the various family members in turn, he decided to ask his friend Hercule Poirot to investigate.
Enthwistle is played by Robert Bathurst in the film adaptation of the book in ITV's Agatha Christie's Poirot series. In the novel Enthwistle handles most of the preliminary investigation and only brings in Poirot in chapter 7. In the film he brings in Poirot almost immediately after Cora's murder, although he continues to play a major role by accompanying Poirot to speak to the family members. In the film, the character is given a first name "Gilbert" which is not found in the book. He also has a fondness for Helen Abernethie, insisting that Helen could not have been guilty of any murder, so much so that Poirot has to remind him not to let his affections cloud his judgment.