'Fiery the angels fell; slow thunder rolled around their shores, burning with the fires of Orc.' Whether in recent popular culture, or back across countless centuries, angels have perpetually enthralled and even terrified us. 'Every single angel is terrible, ' wrote the German Romantic poet Rilke: 'and so I hold myself back from the dark bird-cry of my anguished sobbing.' For sceptics, angels may be no more than metaphors: poetic devices to convey,...