Part 4 - 'The Hairless Mexican', originally transmitted on BBC1 on 8/12/1991

Now an old man and living in the south of France, Ashenden is angered when he hears an old song played on the radio in a new arrangement. He thinks back to 1918. He returned to Britain to help his friend Lehman, who had been arrested after being found in a hotel room with another man. Despite the dangers to himself, Ashenden decides to pay for Lehman's defence. At the Foreign Office, Ashenden meets the head of MI6, who once turned him down for a job. He did this not for the service but to try and save Ashenden himself. Ashenden visits his lover but discovers that she is now seeing someone else.

'R' sends Ashenden to Naples to retrieve coded letters from a courier in the employ of the Turks. Ashenden is to supervise the work of Mexican assassin Carmona, who will intercept the letters and get rid of the courier. In Naples, Ashenden meets Aileen, an American tourist. He invites her to dinner, and later they stop at a shop and look at a statue of a weeping boy. The next day, in the piazza, Carmona tells him that Aileen is the courier and that he has found coded letters in her luggage. Ashenden refuses to believe this and walks in a daze, listening to a waltz played on an accordion by a street musician. He cables 'R' for confirmation.

At dinner that night, Aileen mentions that she only got the tickets at the last minute and that they were originally meant for someone else. Ashenden tries to find Carmona to tell him of the mistake, but can't find him. Later that night, Carmona comes to his room, but refuses to believe that Aileen wasn't the spy. They search her room and find the rest of the coded documents. Carmona is in high spirits and takes Ashenden to a late-night restaurant to eat and dance. The music played there is the same waltz that Ashenden heard on the piazza and which he now associates with Aileen.

In London, Ashenden learns that Lehman won the case, but won't be allowed back in the country. 'R' accepts Ashenden's resignation, telling him that the coded documents were merely knitting patterns. As an old man, Ashenden is still haunted by memories of Aileen. The statue of the weeping boy is now in his garden. He recalls his first meeting with Cumming.