In the novel Death on the Nile, James “Jim” Lechdale Fanthorp is a solicitor living at Glasmore House, Market Donnington in Northamptonshire. His uncle, William Carmichael, was one of Linnet Ridgeway's English solicitors.
When trying to match the names on the passenger list with the faces in the dining room, Mrs Allerton describes Mr Fanthorp as an "intensely quiet young man who never speaks". According to her, he has rather "a nice face, cautious and intelligent". Poirot agrees that Mr Fanthorp is intelligent, saying that he does not talk, but he listens very attentively and also watches.
Poirot also observes that Mr Fanthorp wears the same tie as Hastings. Mr Fanthorp says that it is "an O.E. tie".
Mr Fanthorp sees Andrew Pennington giving Linnet some papers to sign, and he expresses admiration for her habit of reading each document before signing.
On the evening of the murder, Mr Fanthorp is in the saloon, and assists Cornelia Robson in looking for Miss Van Schuyler's velvet stole. However, they are unable to find it. He later remains in the saloon, reading a book entitled Europe from Within. However, when he sees that Jacqueline de Bellefort is working up for a scene, he leaves the saloon, and stands outside on the deck, on the starboard side.
After Jacqueline fires a shot at Simon Doyle, Cornelia runs out to get help, and Mr Fanthorp returns to the saloon with her. At Simon's request, Mr Fanthorp and Cornelia help Jacqueline back to her cabin. Mr Fanthorp stays with Jacqueline while Cornelia fetches Miss Bowers.
Mr Fanthorp gets Dr Bessner to attend to Simon, and helps the doctor move Simon to his cabin. At Simond's request, he returns to the saloon to retrieve the gun, but is unable to find it.
After that, Mr Fanthorp returns to his cabin, which is "number twenty-two on the starboard side -- the one nearest the saloon".
Towards the end of the novel, Mr Fanthorp explains to Poirot and Colonel Race that his uncle, Mr Carmichael, was suspicious of Andrew Pennington. Some of Mr Pennington's explanations of the disposal of funds aroused Mr Carmichael's distrust. When he received a letter from Linnet saying that she had unexpectedly run into Mr Pennington in Egypt, his suspicions became acute. However, he had no definite evidence, and the only thing he could think of was to send Mr Fanthorp to Egypt, with instructions to "discover what was in the wind", and act summarily if necessary.
He had been at Eton.
Farnthorp does not appear in the 1978 Ustinov film adaptation. Part of his role and lines are given to Colonel Race who, in this adaptation, says that he is partly working on behalf of Linnet's English solicitors. The role of being called to the scene after Simon Doyle is shot and helping Dr Bessner move Simon to the doctor's room is however given to Mr Ferguson who in this adaptation has the first name "Jim" in a nod to Fanthorp's first name.