In the novel Dumb Witness, John is an employee at Gabler & Stretcher in Market Basing. He is described as being a "lanky youth".
When Poirot and Hastings come to the office of Gabler & Stretcher to ask for particulars of Littlegreen House, Miss Jenkins asks John if he knows anything about the house. He tells her that he does not, but that the particulars should be in the file.