The utterly compelling new novel from the Sunday Times bestselling author of LIBRARY OF THE DEAD. Abbey of Ruac, rural France: A medieval script is discovered hidden behind an antique bookcase. Within its pages lies a fanciful tale of a painted cave, the secrets it contains - and a rudimentary map. Intrigued, Hugo and archaeologist Luc Simard go exploring. When they discover a vast network of prehistoric caves they realise that they've stumbled across something extraordinary. But as they begin to unlock the ancient secrets the caves hold, they find themselves at the centre of a dangerous game.