In the short story The Witness for the Prosecution, Mr Mayherne is a solicitor working for the defence during the trial of Leonard Vole.
He is one of the main character and he explains to Vole what he is being changed for and the evidence against him. He gets the history that Leonard had with Emily French and lets him know the difference between his statement and Janet Mackenzie. Mayherne than meets with Romaine, Vole’s common law wife. He sees her as a cold distant woman, when she declares him guilty he feels that something is hiding, Sir Charles the Lawyer claims all he can think is that a nephew of Miss French could have done it but little evidence exists. As Mayherne fears for Leonard’s life, a letter comes in and he meets a woman with a massive scar that her boyfriend did after Romaine stolen him, with the letters she wrote to the boyfriend, Mayherne gives the letters to Sir Charles who uses them against the Prosecution and freed Vole. However Mayherne realises that Romaine was the Scarred Woman all along and that gave him the letters and she admits she did out of love and that Leonard was guilty.
While most productions focus less on his personal life, it's said in the story he has a unnamed wife, who notices his habit of over polishing his pince-nez.
The character was later reworked into the character Mr Mayhew, for Christie's own stage adaptation.