After a fire tears through the library of an ancient monastery a medieval script is discovered hidden behind an antique bookcase. Badly damaged, it is sent to Paris for restoration and there literary historian Hugo Pineau begins to decipher the startling fourteenth-century text. Within its pages lies a fanciful tale of a painted cave and a rudimentary map. Intrigued, Hugo enlists the help of archaeologist Luc Simard and the two men embark on a journey that will change the course of their lives forever.

When Luc and Hugo discover a vast network of prehistoric caves, buried deep within the cliffs, they realize that they’ve stumbled across something extraordinary. And at the very core of the labyrinth lies the most astonishing chamber of all, the tenth chamber. Aware of the significance of their discovery, they set up camp with a team of experts, determined to bring their find to the world. But as they begin to unlock the ancient secret the cavern holds, they find themselves at the center of a dangerous game. One ‘accidental’ death leads to another and it soon becomes clear that someone or something will stop at nothing to protect the secret of the tenth chamber.