The center of the story form two boys and two girls who solve puzzling cases regarding horses. A particular enticement to reading are the questions at the end of each chapter, which involve the reader in the action. The answer helps to solve the case. The questions can be solved by using a special decoder, which is included with the books. So readers can decode this secret writing and feel like a pony detective themselves. Luke, Finja, Mimi and Bastian are really mad! An extortionist threatens the feed producer Juergens. Poison has already been discovered in a load of horse feed. The four pony detectives really want to stop the criminal. But where should they start to investigate?