Alas, Francophiles, don’t be seduced by the title – there’s not a croissant in sight in Jostein Gaarder’s latest novel about two former loved-up Norwegians who meet again, seemingly by accident, more than 30 years after they parted. Compelled to revisit the mysterious incident that unravelled them, and moved by an enduring attraction (despite both marrying other people), they rekindle contact via email and begin trawling over shared memories and conflicting beliefs.

Gaarder returns to the philosophical terrain of his blockbuster 90s novel, Sophie's World, to explore the relationship between Solrun, a teacher and Christian spiritualist, and Steinn, a climate change expert and agnostic. Can science explain everything or are there higher forces at work in our lives?

Like the Magritte painting of the same name, depicting a castle floating inexplicably above the sea, Gaarder leaves readers up in the air as to whose view of life we should favour. Perhaps he is suggesting that for many of us, an equally inexplicable question mark floats over the nature of existence. A moving, if slightly bizarre, ending will keep readers guessing.