The Doctor plans on taking Peri to the grand opening of Kew Gardens but as per usual, things don't go exactly to plan and they find themselves at the forefront of the struggle of the industrial revolution. This week, Paddy and Tricia follow The Doctor and Peri as they attempt to find out who is trying to sabotage the next step in human progress. However, a couple of old faces from The Doctor's past are also at play, planning to dominate humanity with The Mark of the Rani.