I, Lucifer by Glen Duncan
http://www.amazon.co.uk/I-Lucifer-Gl...e=UTF8&s=books
Glen Duncan’s I, Lucifer begins one steamy summer as some heavy negotiations are taking place in Heaven. God has decided to give Lucifer, the furthest-fallen of all fallen angels, a second chance. The Prince of Darkness can return to the fold, provided he manages to last one month on earth without sin. The human form chosen for this celestial experiment? A depressed novelist of little renown, currently contemplating suicide in his Clerkenwell garret.