Joan Hargreaves is a non-canonical character who was created for the 2004 ITV adaptation of "The Murder at the Vicarage". Played by Emily Bruni, the character is roughly the equivalent to Gladys Cram in the original novel but has a totally different background and a larger role. For most of the show, Joan had adopted the false name of “Helene Dufosse” and posed as the grand daughter of Augustin Dufosse. Both of them were guests at Old Hall where the older Dufosse is studying and publishing articles about English country houses for a magazine.
Dufosse's cover is later blown when Inspector Slack discovers that the magazine he claims to work for closed down before the war. Joan tells Slack that she and Dufosse are at Old Hall to collect evidence against Colonel Protheroe for an act of treachery he committed during the war.
Joan worked in Special Operations during the war and worked with the French resistance. She met and got engaged to a resistance member named "Henri," who was Augustin's grandson. Protheroe had a desk job in charge of supply drops to the resistance members in Henri's region. One night, Henri and Joan had waited for a scheduled drop of a large sum of French francs but the aircraft dropped the load somewhere else. It turned out that Protheroe had been in league with one "Lacombe", another member of the resistance. Protheroe had diverted the flight to drop the money somewhere else so that Lacombe could pick the money up and divide the money between the two of them after the war. Lacombe later betrayed Henri and Joan to the Germans. Joan had escaped but Henri was executed.
Dufosse and Joan had found the evidence of Protheroe's treachery in his safe and presented them to Slack during the questioning.