Michael Paleologus, retired archaeologist and supposed descendant of the last Emperors of Byzantium, lives alone in a remote and rambling house in Cornwall. His son, Nicholas, is summoned to resolve a dispute which threatens to set his brothers and sisters against their aged and irascible father. An overly generous offer has been made for the house, but Michael refuses to sell.

Only after the stalemate is tragically broken do Nick and his siblings discover why their father was bound at all costs to reject the offer. Their desperate efforts to conceal the truth drag them into a deadly conflict with an unseen enemy, who seems as determined to force them into a confrontation with their family’s past as he is to conceal his own identity.

Synchronicity is as strange a concept as it is a word. In a literary context, it’s about the mysterious tendency of writers to have similar ideas at the same time. It’s as if, for those ideas, the time has simply come. How else to explain Rosslyn Chapel and Knights Templar mythology cropping up in Days Without Number, published in this country in the same month of the same year as The Da Vinci Code, famous now for its exploration of such material? Well, that’s synchronicity for you.

But it only takes us so far, because Days Without Number develops the material in a unique way which some would probably say was typically Goddardian.

I’d known for some time that, bizarrely, the last known descendant of the last emperor of Byzantium died in Cornwall. You can go to the quiet, tucked-away churchyard at Landulph and wonder at the strangeness of how Theodore Paleologus came to end his days there. Then you can travel on west to St Neot and admire the astonishingly well-preserved medieval stained glass in the village church. And, if you have a mind to, you can head north from there to the coast and marvel at the bleakness and the enigma of the ruined Arthurian castle at Tintagel. In so doing, you’ll be visiting three sites whose histories (partly documented, partly imagined) are crucial to the story I tell in this book.

The idea that connects them formed in my mind as I considered the beguiling improbability of the Byzantine imperial line dying out in Cornwall two centuries after the fall of Constantinople to the Ottoman Turks. There’s just no good reason to suppose it really did die with Theodore Paleologus, you see. Just as we can’t be certain it was merely a combination of chance and circumstance that led him to such an obscure corner of the continent in the first place. I certainly didn’t suppose that when I set about devising the plot of Days Without Number. Quite the reverse.

The title Days Without Number actually contains the key to the plot, compressed in just three words. You could call that a code if you like. And there’s only one sure way to crack it.