Outlander season 7, episode 6 reveals that the "Nuckelavee" haunting Lallybroch is actually William Buccleigh Mackenzie, Roger's ancestor. Buck Mackenzie was introduced as an antagonist in earlier seasons. The episode hints at Buck's time-traveling abilities, which will likely be explained further in season 7. Roger's violent reaction to seeing Buck again stems from their history in the 18th century, where Buck tried to have him hanged. Diarmaid Murtagh now portrays Buck, replacing Graham McTavish's cameo in season 5. The recasting may be due to upcoming storylines involving Buck in season 7.