Fluid link K7

Fluid link K7 was a fluid link belonging to the Doctor's TARDIS. The First Doctor falsely claimed that the fluid link had run out of mercury as a ruse to explore the Dalek City. The link was later confiscated by the Daleks and accidentally left behind in the city, forcing the time travellers to help the Thals fight the Daleks to recover it. (TV: The Daleks)