Teenage sisters Annabel and Maureen Brighton receive a mysterious inheritance from their mother. The shoebox contains a letter, one folded tapestry marked ‘Maureen’, and a giant crystal with a mermaid handle. They are instructed to get to Aventurine to find Annabel’s lost tapestry. When they arrive, they discover an enchanted land ruled by benevolent queens with magical creatures, singing horses, and river maidens. Along the way, the sisters find their own magic along with friends, enemies, and love. They learn to use their powers to save the natural world and discover what it means to be coded for greatness.