A plot arc that was incomplete and forgotten, and then suddenly brought back out of the blue to continue the plot arc itself. This is distinct from the Continuity Cavalcade and Continuity Porn tropes in that it's not just a Shout-Out type situation - the plot arc is resumed, essentially where it left off. In short, what distinguishes Plot Archaeology from similar tropes is that it's not just a one-episode reappearance as a Shout-Out. Examples of Plot Archaeology include: