The Castle of Mirrors (2005) is the fourth novel in the Children of the Red King series by Jenny Nimmo. It has a different title in the North America, titled Charlie Bone and the Castle of Mirrors.
Charlie's magical gifts begin to take on a new dimension, as he attempts to escape a ghostly horse loose in the castle ruin. Strange new characters emerge, such as teacher Tantalus Ebony, florist Alice Angel and student Joshua Tilpin, who possesses the power of magnetism. Meanwhile, Charlie's close friend Olivia begins to suffer a crisis when she is turned down for a movie role, and Billy Raven is ecstatic to be offered a home with the De Greys, although with devastating consequences. Charlie also comes a few steps closer to finding his lost father.
The book begins in old Ezekiel's laboratory where he, Manfred and the great-aunts are performing an experiment. They are trying to bring Ezekial's ancestor Borlath back to life. Asa has found Borlath's heart in a coffin with the letter B on it. They put the heart on the horse, Hamaran, but then Manfred sneezes and the horse comes to life, but not Borlath. Downstairs, the horse appears outside Billy Raven's window. At school, Charlie is talking in the hall and has to write lines and bring them to Manfred's office. Charlie then loses his trumpet and spends the morning looking for it. He meets the creepy new music teacher, Tantalus Ebony. He also meets the new students, magnetic Joshua Tilpin (And he doesn't just attract metal!) and telekinetic twins Idith and Inez Branko. Charlie asks Manfred where his office is so he can bring his lines there. Manfred replied in a riddle: "I am behind masks, under a wing, etc." Lysander pulls Charlie aside after homework and says he knows where the office is. Billy Raven says, "Can I come with you?" Manfred says, "Billy Raven, I'd like to speak with you." Lysander tells Charlie that the office is behind a bookcase. Charlie goes to find the mentioned bookcase and he meets Billy, who cheerfully tells him that he is being adopted by Florence and Usher de Grey. He then asks about Charlie's wand. Billy guesses it is under the mattress. Charlie feels uncomfortable and goes to find the bookcase. Billy steals Charlie's wand and gives it to Manfred who burns it, turning it to a moth. Billy's new parents are mean. With the help of the flames, he escapes. Charlie takes him to the castle of mirrors, where he finds a man and mistakes him for his dad. Billy's godfather and Charlie's uncle finds them. Suddenly, Charlie's uncle's great granddad tries to kill him, but Billy's godfather pushes him and they both fall to their deaths. Olivia finds out she is endowed with the power of illusions. She scares Dr. Bloor into letting Billy stay where he wants.