The Relic Hunters (Grey Griffins: The Clockwork Chronicles Series #2)

In just one semester at Iron Bridge Academy, The Grey Griffins have already had quite an education-clockwork robots, students with super powers, and a hidden land beyond our world where mystical creatures and incredible inventions exist. But as second semester begins, their friendship is put to the test-Max, Ernie, Natalia, and Harley are growing apart. When their arch nemesis Otto Von Strife reemerges with another evil plan, the Griffins must learn to set aside their differences and reunite to save the world. And each other.