Episode Title:
Missing Link.
Episode Description:
During a mission to Sector 5, the Scyphozoa attacks Yumi, stealing her human DNA, leaving her trapped on Lyoko. To make matters worse, it's picture day for her class and she will be suspended if absent. After some discussion, Ulrich gets the idea to have Sissi stand in for Yumi. Strangely, Sissi agrees and asks for nothing in return. During this, Jeremy tries to come up with a way to bring Yumi back. Aelita thinks of a way, but will not tell Jeremy about it. She only tells him once on Lyoko, so he cannot object. She begins to transfer her own genetic code to Yumi, which will let X.A.N.A. take her memory at will, and thus will be exposed. Luckily, Odd and Ulrich get there in time to stop her. Meanwhile, Jeremy figures out that Yumi's human DNA code should be stored in X.A.N.A.'s memory, which is accessible through Sector 5.
