Justin is a pious Christian knight from medieval England, transported to the 20th century by the demon Melanicus, where he collides with the TARDIS outside of the village of Stockbridge. Having been brought into the TARDIS, Justin believes the Doctor to be an angel of God, the TARDIS a miracle and their quest a crusade, despite the Doctor's attempts to persuade him otherwise. Eventually, with the help of Rassilon, Merlin, and the Matrix-powered Time Lord agent known as Shayde, the Doctor confronts Melanicus in a time-altered version of a Stockbridge church. During the ensuing fight the Doctor is knocked unconscious, while Justin kills Melanicus at the cost of his own life.