Landing on the generation ship Not-Home, Steven and the Doctor find the TARDIS drained of power and unable to take off again for months, if not years. They meet Korra, an inhabitant of Not-Home who carries a Helmstone - an artifact that requires her to present herself at the city for a ritual. The three of them undergo the journey together, but the Doctor and Steven suspect that all is not as it seems... Helmstone was a short trip featuring the First Doctor and Steven Taylor which was available to subscribers of Big Finish's main Doctor Who range whose subscription included The Silurian Candidate and Time in Office.