What special power do Matt and Emily Calder share?
Where do Matt and Emily flee to for safety?
What is the name of the hidden realm said to contain all the world's mythical creatures?
Who is responsible for helping the twins understand and control their powers?
Why are the twins hunted by dangerous enemies?
What kind of bond allows Matt and Emily to strengthen each other's abilities?
What organization seeks to control or use the twins for their own ends?
What is the risk of opening Hollow Earth?
What type of art do the twins use to access their powers?
What secret does the twins' mother keep from them at the start of the story?