Corey's Pony Is Missing

When Corey goes to visit her father for a few days, May and Jasmine promise to keep an eye on her pony. Corey hates to leave Samurai behind, but she knows that no one could take better care of Sam than her two pony-crazy friends in the Pony Tails.
Then, shortly after Corey leaves, Sam disappears from his stall. What has happened to Corey's pony? And how could May and Jasmine have let Sam get away?