First I would find the episode or likely episode in one of these lists: https://en.wikipedia.org/wiki/List_of_Horizon_episodes https://en.wikipedia.org/wiki/Li

First I would find the episode or likely episode in one of these lists: https://en.wikipedia.org/wiki/List_of_Horizon_episodes https://en.wikipedia.org/wiki/List_of_Horizon_episodes https://www.imdb.com/title/tt0318224/episodes?ref_=tt_eps_sm https://www.imdb.com/title/tt0318224/episodes?ref_=tt_eps_sm Then hunt for that episode. There are a lot of episode online. For instance: https://archive.org/details/BBCHorizonCollection512Episodes https://archive.org/details/BBCHorizonCollection512Episodes