S04E30 — Echoes

With their mission completed, the group looks back on all their fond memories of Lyoko. Sissi, meanwhile, plants a tracking device on Ulrich in order to discover their secret. When it comes time to shut down the supercomputer, all but Yumi are unwilling to go through with it: Aelita is still holding onto the hope that her father can somehow be saved, Jeremie doesn't want to take away the thing which made them friends, and Odd and Ulrich both liked being heroes. While they muse over their attachments to Lyoko, Sissi finds her way into the computer lab, and Jeremie's open diary reveals the whole of their adventures. When Sissi tries to explain this to her father, he believes she has lost it and sends her to the infirmary. A return to the past deals with that problem. Ulrich stops Sissi from planting the tracker on the repeat attempt, and the quintet invites her as a friend. Once more at the supercomputer, the group unanimously decides to shut it down, closing the book on their adventures, for now.