Set in the world of Irish mythology and faery tales, this story tells of the coming of the Great Queen, the Morrigan, from out of the west to free the snake and bring destruction to the world. When ten-year-old Pidge finds the crumbling pages of an old manuscript in a second-hand bookshop in Galway, he unwittingly releases the serpent Olc-Glas and the forces of good and evil gather to do battle. The Morrigan, goddess of death and destruction, has set her evil heart on gaining Olc-Glas and adding its poison to her own, thereby casting her shadow over the world. Pidge and Brigit are chosen to thwart the Morrigan, and so encounter many adventures on the way, as well as meeting an array of unforgettable characters.