Star Flower

Thirteen-year-old Stella is not like other girls. She helps her dad at the flower shop, her chatter in her mom's native language makes the plants flourish, and she understands at a glance what is ailing the azalea.
 
One day, Stella meets... a man in a top hat who assures her that she is a plant sorceress, and her mom was supposed to leave her a key. The girl doesn't believe him, but... there really is a key in the attic. How did it end up in her mom's things? Stella decides to keep the discovery to herself.
 
The next day, the girl walks home from school with the new kid, Kian. They chat sweetly until the boy suggests opening a door with the key from the attic. It turns out that Kian was sent by the man in the top hat! Stella ends up in a magical world of caves with strange creatures and inhabitants. Will she be able to return home? And why can only a plant sorceress find the star flower?