Curse of Trevalia (Trevalian Magic, Book 2)

The Trevalian Cubes are more than they seem. They hold a powerful magic, yes, but there is more... A secret has been hidden for centuries. This secret must at last be revealed as an ancient and powerful enemy is set to free himself from the prison he was condemned to long ago.
Once again, the magic of the Cubes call to Danny and Susan. The need is great, though. Perhaps there are others who must be called, as well. Will even those called as allies be enough to stop the evil wizard Canthos as...