This book is Carson's most ambitious book to date. Like 'Fishing for Amber', it delights in stories and their meandering connections with an infinity of other stories. 'The Arnolfini Portrait' is at the center of the book, the great van Eyck painting of a merchant and his wife in the city of Bruges. Around the painting swirls a galaxy of esoteric and entertaining knowledge of saints' days, herbal cures, animal symbolism, miracles and transformations.

Shamrock Tea, the magical substance that allows people to experience the world with visionary clarity, can only be found by passing through the van Eyck painting into another world. The characters who bear this knowledge include a young boy called Carson, his uncle Celestine, his cousin Berenice, Ludwig Wittgenstein, Father Brown, and young Maeterlinck, the nephew of Maurice Maeterlinck, an art-dealer in the Flemish city of Ghent. Everything connects with everything else: one of the book's presiding geniuses is Arthur Conan Doyle, who believed that you could read the world in a drop of water.

Shamrock Tea is an homage to this idea, to an almost medieval sense of the unity of the world - what in other words we call magic.