AVAILABLE JULY 2021. Written by Simon Guerrier. Starring Jon Culshaw. In the depths of the ocean on an alien world, there’s a city run by scientists. The Doctor is only too eager to help them find new ways to counter pollution and produce entirely clean energy – research that he says will benefit the whole galaxy. But others have recognised the value of the sea base, and their interest is not so benign… *This enhanced audiobook features specially composed music and sound effects.