Do you like a mystery? A conspiracy? Well today we have a report from the Carcassonne region of France, sent in by our doughty French Decorating correspondent. He filed this picture with the information that “it was taken through the glass of a locked room.” Chills.

The wallpaper’s origins we’ll come to in a minute. The photograph was taken at Rennes Le Chateau, a hilltop village in southern France which has been a haunt of treasure hunters and conspiracy theorists since the 1950s.

At the end of the 19th century the village priest there, Bérenger Saunière, began spending vastly more than he earned. On a priest’s salary of 900 Francs a year, records show his outgoings often exceeded 50,000 Francs a month. Theories as to the source of the money range from dodgy payments to say Mass (but 50,000 Francs worth is a lot of Mass, even if you’re really racing through it) to a discovery of buried treasure. Read all about it in convoluted detail here, if you have all day.

I – like the 10,000 treasure hunters who visit the village each year – have no answers about the source of the riches. But I do have an inkling where he might have spent some of the 50,000 Francs. The wallpaper, it turns out, is by Alphonse Mucha. It looks to my untrained eye like the psychedelic-pastoral style favoured in my 1970s childhood. But in fact it is a non-repeating wallpaper by the inventor of Art Nouveau. The image above is more typical of his style. All we can really say for sure is that the priest was really going for it on the decorating front. Bit like if I’d papered a bedroom with Hirst Spot Paintings – it can’t have come cheap.