I really enjoyed reading this. It is a serious, well documented, and sober exposition of the angelic world.
"Dr. Harry Boosalis, in this concise text, presents us with the Scriptural and Patristic teaching of the Church on the heavenly hosts of angels, the devil and his demons, and the enigma of evil.He offers a rich deposit of Tradition in simplified language, in a clear and concise style, but with an extensive body of scholarly documentation in the footnotes." From the STOTS website