Ambrose Meyrick is at first a pupil at a hateful English public school, then a young man at large in bohemian London. Throughout his adventures, Ambrose cherishes his childhood vision of the mystical cup of Teilo Sant. But the young man also displays a fine delight in the good things the world can offer, and a few weeks spent with school servant Nellie Foran in a London lodging house prove a turning point in his life.
Ambrose, in retrospect, considers himself to have sinned, and he returns home to his native Wales. In writing of great beauty and power Machen describes how Ambrose rediscovers the magical Gwent countryside, and performs the marriage of the cup with Sylvia, his symbolic muse.