When a mysterious island emerges from the River Riddle, panic spreads through Owlchurch. It's the Island of Ghosts, where ghosts of past Rymers dwell in afterlife. Its appearance means only one thing: a living Rymer is in mortal danger. Only one known Rymer lives. Thomas Trew. A plan is quickly hatched to send Thomas back to London where he is safe from the dangers of the Hidden World, but Thomas has other ideas. He loves living in Owlchurch - now his real home - and can't bear to leave all his new friends for boring, dreary London. Thomas soon devises his own daring plan to search the island to seek his mother, Mab, a past Rymer whose ghost must live there. And so awaits a dark and dangerous adventure as Thomas enters the island's door ...