It is summer and the long holidays at Golden House stretch before William, Mary and Alice Constant. Hot lazy days of swimming and picnics . . . until a new and terrible shadow steals over the valley and the children are plunged into a desperate adventure to save it from greedy developers. Once more they are pulled into the Magician's world and his eternal battle between good and evil. But without the Magician's trust and with evil Morden's powers now stronger than ever, they have a huge task on their hands.

William, Mary and Alice Constant have come to spend Christmas with their uncle as their parents are working abroad. Little by little, they discover that things in this remote old house are not quite what they seem. There are powerful forces at work, calling to the children from across the centuries; forces that pull them up the hidden steps in the chimney to the secret room where the magician lives.

It is spring and William, Mary and Alice Constant have returned to Golden House for the Easter holidays, anxious to see if the magic will work again. When they are drawn to the Magician's hideout, through a door in a tree, they learn that the secret to magic is believing; and through believing they can enter the magic and continue their great task.

It is deep autumn and William, Mary and Alice Constant have returned to Golden House for the half-term holidays. At once they are thrown into the most crucial and desperate adventure of all. Matthew Morden is on the point of discovering for himself the art of time travel and his evil influence is permeating the whole valley. Now the future of the valley depends on the children reaching the Magician in his own time. The time has come for a final confrontation; the last great battle is about to be fought.