The moonlight market / Joanne Harris.

Orphaned, lonely, and lost in his photography work, Tom has no intention of falling in love. And yet, love finds him in the shape of beautiful Vanessa, who lives a dangerous double life in the heart of London's King's Cross. Tom's pursuit of Vanessa leads him to discover an alternate world, hidden amongst the streets and rooftops of London - and inhabited by strange and colourful beings. In this mysterious realm, two ancient factions - one of night, one of day - have waged war for centuries over a forbidden love and a long-lost prince of sun and starlight. But when Tom finds a secret market that appears only in moonlight, where charms and spells are bought with memories, he starts to wonder whether he's been here before.