For Kicks by Dick Francis

The source material is comprised of excerpts from the novel For Kicks, centering on the covert investigation led by protagonist Daniel Roke, a former Australian stud owner. Roke is hired by British racing Steward Lord October to infiltrate a sophisticated horse doping scheme after the conventional testing methods fail to identify the drug being used on several race winners. Roke adopts a tough, "cockney-Australian" persona to work as a stable lad in both Lord October's yard and the abusive stable of suspect Hedley Humber, leading him to identify the chief culprit as the violent owner, Paul James Adams. The central discovery is that the horses are not drugged, but psychologically conditioned to panic and sprint upon hearing a high-pitched dog whistle, a reaction amplified by the prior terror of a flame thrower. The mission ends violently when Roke kills Adams in self-defense and rescues October’s daughter, Elinor Tarren, who had been incapacitated by Adams to silence Roke’s allies.