Saint Marie is described in Episode 3.3 as a "pretty island" that is "situated in the Eastern Caribbean Sea" and "one-tenth the size of its north-west neighbour Guadeloupe", which would make Saint Marie about 63 square miles (160 km2) in size. It is described in Episode 4.5 as being 70 miles from Martinique.

The island is a British Overseas Territory, but was handed over to the British from the French only in the 1970s, so that about 30% of its people are French citizens, with the French language still widely spoken.

The back-story appears to be a blend of two real-world islands near to Guadeloupe, with size and location aligning with Marie-Galante (in real-life politically affiliated with Guadeloupe, not independent of it), and history and language aligning with Dominica. Another possible basis is Îlet Sainte Marie[original research?] "The Îlet Sainte-Marie is an island located on the northeast coast of Martinique, right in front of the small town of Sainte-Marie, known in the North Atlantic region. Very popular with tourists, it is a geological curiosity of nature, as connected to the rest of the island by a tombolo."[1]

They drive on the same side of the road as the UK,[2] but vehicles, including the police Land Rover Defender 110, have number plates the same format as the vehicle registration plates of France.