Used book – Seven Days for an Eternity..., Marc Levy

To put an end to their eternal rivalry, God and Lucifer set each other one last challenge... They send their two best agents on a mission... Lucas and Zofia will have seven days on Earth to make their side triumph, thus deciding whether Good or Evil will govern humanity... In organizing this absurd wager, God and Lucifer had foreseen everything, except one thing... That the angel and the demon would meet...

9782266136044