When Emily makes a wish on a magic stone, she gets a glimpse of what the future holds -- and it's a disaster! She tries to make things right, but each trip through time takes Emily to a future where things turn out badly for either the humans of Brightport or the merpeople of Shiprock. Plastic pollutes the ocean, garbage overflows the landfills, and the two towns are no longer getting along. Emily realizes she can't save her hometown and the ocean alone, but with help from her best friends, Shona and Mandy, she'll have to find a way to get humans and merpeople to work together.