In the remote Irish woods, Cellach (Brendan Gleeson) prepares a fortress for an impending attack by a Viking war party. Unbeknown to Cellach, his young nephew Brendan (Evan McGuire) – who has no taste for battle – works secretly as an apprentice in the scriptorium of the local monastery, learning the ancient art of calligraphy.
As the Vikings approach, revered illuminator Aidan (Mick Lally) arrives at the monastery and recruits Brendan to complete a series of dangerous, magical tasks.