Although, it was the modern series which formally introduced over-reaching story arcs, the classic series occasionally dabbled in that area such as in 1979's so-called E-Space trilogy, a series of, er, three linked adventures which saw the TARDIS lost in a universe separate, though tied, to our own. Sucked through a Charged Vacuum Emboitment (catchy!) from N-Space, our universe, the Fourth Doctor, Romana and K-9 had several adventures in E-Space including meeting a new friend, Adric, in Full Circle and battling the Time Lords' ancient enemies the Vampires in State of Decay before the Doctor finally left the universe in Warrior's Gate, albeit without Romana and K-9 who elected to stay behind and help the persecuted Tharils. Well, Romana did. K-9 was just sort of kicked out the TARDIS. Apart from being a rare earlier example of plot threads weaving through multiple stories, this trilogy also acts as important series of sideways Doctor Who episodes as they gave the Doctor a whole new universe to explore and leave unwanted robot dogs in.
