Someone in Hertford is now claiming to be the Templar order, which they say went underground when the church suppressed it; furthermore, they have written to the Vatican, demanding an apology for their persecution, and claim that "things are about to happen that will deserve attention".
"The vast majority of Templars either escaped, or didn't escape, but survived," Acheson says. So how did they end up in Hertford? History records that a number of them were imprisoned in Hertford Castle, but how did Hertford become a centre of operations? "I can't really tell you that. All I can tell you - it's going to be quite vague - is that they flourished in western Europe." He explains that there is a stained-glass window in St Andrew's Church, just down the street, that contains a clear metaphorical allusion to the Holy Grail, and a cryptic hint that it might be hidden in Hertford. In the picture, Acheson adds, Jesus and Mary Magdalene are looking at each other "in a very meaningful way". (Later, I find the window, interrupting local parishioners who are decorating the church for Christmas. I think I can see what Acheson means about Jesus's expression, although mainly he just looks a bit depressed.)
Public accountability is a laudable goal, but it's hardly something you expect from the secret rulers of the universe. Indeed, when a group of amateur archaeologists recently announced their intention to investigate Hertford's tunnel network, someone posted a message on a local website warning that anyone who tried would be "dealt with". The message read: "Anybody intending to find out more, let alone discover hidden areas of the labyrinth, should check their life insurance policy very carefully indeed."
The tantalisingly mysterious word "labyrinth" in the warning does raise some questions. I wonder whether the upcoming great revelation is going to be a Templarland theme park or similar tourist trap to attract Da Vinci Code fans and the well-off and credulous.
Acheson takes me on a walking tour of Hertford, and proves a knowledgeable guide, but a frustratingly cryptic one, too. So I decide to take matters into my own hands and head for Monsoon. Gemma, the manager, responds far more patiently to Grail-related inquiries than might arguably be her prerogative. There's no tunnel beneath the shop, she insists, "just the store room" - but it's "definitely haunted. When we have sales meetings there you can hear someone walking over our heads, or doing the vacuuming. But upstairs, the shop's closed and empty."