Failure

Best friends Carla and Isa spend their time travelling around the world competing on their horses Cloud, Skye, Fontaine and Grecia.
But one day Carla receives an email telling her to sell Isa's horses Fontaine and Grecia to a mysterious buyer. Failure to comply would result in serious consequences.
There was only one other detail in the email. Carla must win the next dressage cup or she would be killed.