The Postman, who rides a bicycle, appears several times in The Picts and the Martyrs. In PM2 he knocks on the door then hands the letters over, including the letter for Miss Ruth Blackett from the Great Aunt.
The Ds persuade him to leave their letters in the wall (PM7), and see him doing so (PM14). When the GA goes missing, he is apprehensive that the GA will find out that he was delivering the Ds letters addressed to Beckfoot into the hole in the wall instead; with Jacky, Mrs Lewthwaite, Mrs Braithwaite, Billy and Sammy all knowing about the Ds (PM26). He goes to Beckfoot with the searchers (PM29) but does not speak to Nancy.