Twelve-year-old Macy is an amateur treasure hunter who finds lost things along the southern Saskatchewan shores of Buffalo Pound Lake.
When her mom announces she's leaving her park ranger job at the lake to be a police officer in the city, Macy decides she needs to find a treasure big enough to put Buffalo Pound on the map so her family can stay put. But instead of a treasure, Macy finds a mermaid kidnapped from the West Coast and brought to the Prairies by a monster known only as "The Beast." Macy must find a missing magic shell to reconnect the mermaid with her family. But will Macy find the shell before the Beast does?