After an unexplained incident on Lyoko ends up devirtualizing Yumi without any cause, she is taken to the infirmary. After waking up, she attacks Yolanda and continues to act weird throughout the day, wanting to go to Lyoko with everyone else. Jeremie won't let them, though, because he wants to know just what caused her devirtualization. Meanwhile, on Lyoko, Aelita finds several Roachters guarding an orange sphere, which she calls a Guardian, and informs Jeremie. Back at the school, Jean-Pierre confronts Yumi about her attack on Yolanda. When he threatens to call her parents, she attacks him as well. In another attempt to get the group to Lyoko, Yumi tries to seduce Jeremie to convince him to arrange a mission. She fails, but Odd and Ulrich stumble upon the scene. Jeremie tries to explain, leaving Yumi alone. Jeremie apologizes for the incident, citing Yumi's strange behavior. When they head back to his room, they find his computer destroyed. Yumi seems the likely culprit. She shows up to meet them, still wanting to go to Lyoko. Having no choice, they go, but Yumi stops the scanner before it can close, leaving her alone in the scanner room. As she goes to work destroying the scanners, the others find the real Yumi trapped inside the Guardian. After being devirtualized by Ulrich, she and the cloned-Yumi engage in battle. Eventually, the clone tries to kill Jeremie, but Aelita manages to deactivate the tower before Jeremie falls to his death.