In The Case of the Wounded Agent, Maxos was the name, or perhaps codename, of one of Major Charles' best agents in the Balkans. He had been making his way into Northern Greece, pursued by various hostile forces, when he had been hit in the thigh by a bullet. As he was carrying a document which was very important to Major Charles, Biggles was asked to rescue him by air.
For some time, Maxos had been in touch with Major Charles by radio and had reported his position as somewhere between the villages of Demphos and Petritza. By the time Biggles arrived on scene in his Auster, the radio had gone silent. Nonetheless, Biggles spotted him breaking cover and succeeded in picking him up, evading enemy patrols along the way and brought him to Brindisi where Ginger was waiting as backup. Probably because Major Charles or Ginger knew that Maxos was wounded, arrangements had been made for Doctor Spanelli to meet Maxos at the airfield and take care of him. The document Maxos was carrying was then ferried to London by Ginger.