Doctor Who Temporada 12 Episódio 4

1903. On the edge of Niagara Falls, something is wrong at Nikola Teslas generator plant. Who or what is sabotaging the maverick inventors work? Has he really received a message from Mars? And where does his great rival Thomas Edison fit into these events? The Doctor, Yaz, Ryan and Graham must join forces with one of historys great minds to save both him and planet Earth.