Fr. Louth dicusses the origins of Christian theology, especially the "mystical" theology. He doesn't limit himself to the Latin West, thankfully, but rather embraces the Eastern perspective as well. He works through Plato, Philo, Plotinus, Origen, Nicene Orthodoxy (Athanasius and Gregory of Nyssa), the monastic contribution (Evagrius of Pontus, the Marcian homilies, and Diadochus of Photice), Augustine (of course), Denys the Areopagite, Patristic Mysticism and John of the Cross (divine darkness and the Dark Night), the mystical life and the mystical body (Platonism and mysticism, the communion of saints).
Like his other works, this is exhaustive and articulate. A strong dose of the texts themselves, in translation, helps us meet the minds of these influential thinkers at firsthand (almost).
I find his treatment of neo-Platonism most useful. Following Pelikan, Lossky and Florovsky, Louth shows that the Eastern Orthodox tradition was not Hellenized, but that the Hellenic framwork was "baptized" so to speak, but not on a wholesale scale. It was tweaked to fit the revelation of God in Christ.
I would strongly recommend the works of Vladimir Lossky in this regard, especially his The Mystical Theology of the Eastern Church. There are many great books on this subject, but this is a great place to start! Enjoy!