Buttercup Mystery, Paperback/Kristin Earhart

The Dunlap siblings must solve the mystery of a sick pony on Chincoteague Island in this second book of a chapter book series inspired by Marguerite Henry's Misty of Chincoteague . There's a sick horse at Misty InnSomething Buttercup is eating--or being fed--is making her ill. Can Willa and Ben solve this pony problem and help Buttercup feel healthy again?