Biography: When travel writer Jeremy Seal fathered two daughters, the question of Santa Claus's existence inevitably became an issue.
The search for the truth provided Seal with the perfect excuse to wander around Greece, Turkey, Italy, Amsterdam, even Manhattan, following in the footsteps of the man known as Sinterklaas, Agios Nikolaos, Noel Baba and, of course, Santa Claus.
The story begins in Demre - now Myra in Turkey - where Nicholas was bishop circa AD 300. Fast forward 11 centuries to Florence and a fresco by Fra Filippo Lippi depicting a man at the door of a house carrying a sack of goodies.
Santa Claus?
Sort of. The fresco illustrates the story of how Nicholas intervened when a man in Demre, unable to raise the money for his three daughters' dowries, contemplated selling them into prostitution.
Enter Nicholas with a bag of gold coins - no, not to buy the young girls for his own delectation - but for their dowries and a chance to live happily ever after. And because he was a modest man, he came anonymously, under cover of darkness.
This then is the occasion whose annual commemoration, in all its manifestations, either delights or plagues.
But surely Myra is a long way from chimneys, shopping centres and the western world's most commercialised feast? It is, and Santa: A Life traces the route St Nicholas took over the centuries to get to, not only the outer reaches of Europe, but across the Atlantic to New York.
Myra is only two miles from the sea and it was through traders and raiders that Nicholas - his reputation and his bones - travelled to Bari and on to Venice.
His association with sailors is reflected in the number of churches in ports bearing the name St Nicholas of Myra. In Dublin alone there are three.
En route, the relics of Nicholas acquired their powers. He deterred invaders, rescued people from slavery and bits of his body were scattered around the world. In Bari,the fragrant emissions from his bones are collected annually and used for various ailments.
In the Netherlands, he turns up with a black face, exhibiting as the author puts it, "the otherness of the outsider".
The book is rich in anecdote. The author reveals why St Nicholas was low in the saintly league tables in New York and why supporters of St George were more numerous, while St Patrick's crowd were more fervent.
Despite its subject matter, this isn't a family book. Included is a description of the imaginative sexual antics of the consort of the Byzantine emperor, Justinian.
Jump on board if you don't like Christmas. Seal takes us to the lower depths of schmaltz, from grottoes in Birmingham to Finland's frozen north, where his children are given skipping ropes and felt-tip pens.
But why, if he went to Finland, did Seal not touch on another theory: Santa originated in the red-coated Saami who appeared from the northern wastes with their reindeer-drawn sledges laden with the toys and artifacts they had hand-carved in their snowbound tents. That, perhaps, is another story.
Mary Russell is a writer
Santa: A Life By Jeremy Seal. Picador, 233pp. £14.99