To find it, and to uncover the unspeakable mystery, three men venture into the heart of the Sahara. An archaeologist tracing his father’s footsteps, a colonel from the French Foreign Legion hungry for revenge and a priest putting his faith to the test: all three will come face to face with their respective destinies in front of the Tower of Solitude. Meanwhile, the most superb and disturbing of messages echoes across boundaries of time and space.