Down Among the Fearful (2) (S07E02)

While investigating the murder of Vicki Walmsley, Lewis and Hobson receive news of a stolen supply of etorphine from the Garsington Equine Centre. This potent drug had been used a year prior on a horse that hurt its young rider, Joshua Grace, who happens to be the brother-in-law of Reuben Beatty, the initial victim in the murder case.