The Stollen Gem

Focuses on a group of people who can shapeshift into magical creatures. Their job is to protect the human world from dark creatures from other realms. To do this, there is a council that assigns guardians tasked with protecting a magical crystal that keeps the realm doors closed- which is hidden in an underground labyrinth that only guardians can find their ways through. One day the guardians go missing and the crystal is stolen, making the realm doors breachable. So, a group of young shapeshifters are chosen by the council to be the new guardians, and are sent on a journey to track down the creature that stole the crystal before they can open the doors the dark realm.