In Dangerous Freight, Monsieur Laroux was a French tourist who claimed to have come to the Camargue to photograph the flamingoes. He asked to stay at the farm house of Monsieur Vallon, a local farmer, saying that his car had broken down and so happened to be on the scene when a Douglas DC-3 carrying a gold shipment crashed nearby. Vallon rode off to Arles to report the incident while Laroux stayed to do what he could if any of the crew were still alive.
When Biggles arrived at the crash site and was informed that the gold cargo was missing, he reasoned that the thief must be still in the vicinity. He could not have gone south because there was nothing there but salt pans. Nor could he have gone north because he would have met the police and Vallon coming down from Arles. When Biggles learnt from Vallon that he had Laroux staying with him, and that Laroux had been alone at the crash site for almost an hour, suspicions naturally fell on Laroux.
Biggles convinced Marcel and the local French inspector to confront Laroux. The so-called broken down car started without difficulty. Marcel demanded the car keys and found the gold inside the boot. Laroux was arrested and, faced with a possible death sentence as an accessory to murder, confessed and revealed the details of the crime and the gang leaders who were working from Accra in Nigeria, leading also to their arrest.