The Emerald Boy

The islands of MiYu shimmer with magic. Dragons devour rocks and lay shining jewels, ghost owls fly right into your dreams and steal your most treasured memories. There are ravenous shark-mice and mile long sea serpents, sunken cities and spiders so huge their webs span mountains.
"I banish you from our island," the high priest roars. "You may only return when my dear son Smald lives again!"
Opal and Tiger-eye have a problem. A dragon turned their worst enemy in an emerald statue and they are blamed. There is only one way to turn him back: find Smald's own weight in emeralds.
Sadly all such precious jewels are already in use, as the eye of a golden sea serpent for instance or crowning the head of the immortal emperor of Scorpio.