Lois or Clark discovers someone who looks just like them. S/he didn't know s/he had a twin. Perhaps neither did her/his parents (or one that they had ever been mentioned to her, in the case of the Lanes). This person grew up with a different family, but then was locked away sometime when s/he was a teenager (between the ages of 13-19). S/he isn't let out into society again until Lois/Clark stumbles upon her/him during S1 or S2 (so roughly 10 years later).
Who raised the twin? Why was s/he locked up (joined a cult, sent to be raised by monks, imprisoned, Rapunzeled, self-imposed, etc)? How have these events changed the personality of this person? How does s/he differ in personality/looks/temperament/interests from Lois/Clark? Why were the twins separated as infants? Did Sam Lane, upon discovering he wasn't having just one daughter but twins daughters, only keep one and give the other up for adoption? Did Jor-El send two sons to Earth, in the same ship or in separate ships? If in the same ship, how did Kal-El get separated from his brother? (Was Tempus involved?)
Does Lois/Clark get along with this new-found sibling? How does the twin impact Lois and Clark's friendship/relationship/partnership? What if Lois's twin falls for Clark when Lois falls for Luthor (or vice-versa)? What if Clark was one twin and Bruce Wayne the other?
OR
Is this person a twin after-all? Could this "twin" actually be a clone? Was this whole scenario be a set-up to entrap the original or because the cloning process made the "twin" mentally unstable/violent?
