The O Trilogy Series by Maurice Gee

When Nick Quinn goes to spend a couple of weeks on his uncle's farm at Lodestone Creek, he expects it to be like every other summer holiday. His dopey cousin Susan is more remote than ever, but swimming and exploring will make up for the lack of companionship.But Susan is spirited off down a disused mineshaft into the world of O, and is taken prisoner by Odo Cling and the Deathguard. Nick follows to rescue her and the Woodlanders of O come to his aid... moreWhen Nick Quinn goes to spend a couple of weeks on his uncle's farm at Lodestone Creek, he expects it to be like every other summer holiday. His dopey cousin Susan is more remote than ever, but swimming and exploring will make up for the lack of companionship.But Susan is spirited off down a disused mineshaft into the world of O, and is taken prisoner by Odo Cling and the Deathguard. Nick follows to rescue her and the Woodlanders of O come to his aid. They know that Susan is the only one who can save their world, and perhaps her own. less

A hundred turns have passed since Susan Ferris joined the Halves and ended the rule of the Halfmen of O, Otis Claw and Otis Cling. But Humankind has chosen evil a second time. O is now in the hands of the priests of Ferris who use Susan's name to terrorize the world... moreA hundred turns have passed since Susan Ferris joined the Halves and ended the rule of the Halfmen of O, Otis Claw and Otis Cling. But Humankind has chosen evil a second time. O is now in the hands of the priests of Ferris who use Susan's name to terrorize the world.A prophecy among the Stonefolk, dreams of the long-dead Jimmy Jaspers and a great white bear, a flower called Shy, and a message from a girl named Soona all draw Susan back to the world of O where she must face the High Priest and destroy the Temple. Susan is afraid, her task seems impossible, but she is angry too, that her name should be used as an instrument of terror. She wants to rush to the Temple and break it down with her hands, but Soona must be rescued first, and naturally the High Priest has a plan of his own. less

'King,' they said, trying out the word, 'Osro is King. 'Now, stand up,' Osro said. 'Take me to Susan's door. You are my hands and I am your head. Soon O will be ours.' For Susan and Nick the adventure at last seems at an end. They are leaving the magical land of O, the scene of The Halfmen of O and The Priests of Ferris. But even as they prepare to step back to Earth, strange and evil forces reach out to ensnare them. For Susan and for the Motherstone there is one final, frightening task... more'King,' they said, trying out the word, 'Osro is King. 'Now, stand up,' Osro said. 'Take me to Susan's door. You are my hands and I am your head. Soon O will be ours.' For Susan and Nick the adventure at last seems at an end. They are leaving the magical land of O, the scene of The Halfmen of O and The Priests of Ferris. But even as they prepare to step back to Earth, strange and evil forces reach out to ensnare them. For Susan and for the Motherstone there is one final, frightening task. Motherstone is the last thrilling book in Maurice Gee's saga of the world of O. less