Gerald, Cathy and Jimmy are forced to spend the summer holidays at Cathy's school. During a picnic, Gerald makes a discovery which leads them into many strange adventures.

Mabel, the housekeeper's niece at the castle, shows the children the jewel room. When she tries on a ring, her wish to be invisible comes true.

When Gerald tries on the ring, he can see the castle's statues come alive at night. But when Eliza the maid puts it on, things start to go terribly wrong.