When learning about NanoDoctors, small robots being designed to cure dieases, Ulrich holds some gel that the NanoDoctors would live in. Od pranks him and pushes the gel into Ulrich's face, and some minutes later Ulrich suddenly faints and loses his memory. Strangely, amnesia spreads throughout the school, and Jeremy and Od think it's Xana at work. Yumi and Od are virtualized while Ulrich escapes from Sissy, who's trying to convince him they're in love. Ulrich gets virtualized and re-learns how to fight from Od. They help Aileta deactivate the tower. It ends up being the NanoDoctor's gel habitat was infested by Xana Nano-Virii and got up Ulrich's nose.

Fent servir una màquina del laboratori de química, el XANA ha creat uns nanovirus amb la capacitat d'atacar les cèl·lules de la memòria del cervell dels humans. El primer de caure és l'Ulrich. La Sissi se n'aprofitarà: li farà creure que és la seva nòvia i que l'Odd, en Jeremy i la Yumi són els seus enemics.

当 Ulrich 了解到纳米医生（NanoDoctors）--一种被设计用来治疗疾病的小型机器人--时，他拿着一些凝胶。Odd恶作剧地把凝胶推到 Ulrich 的脸上，几分钟后，Ulrich 突然晕倒并失去了记忆。奇怪的是，失忆症传遍了整个学校，Jeremie 和Odd认为是 Xana 在作怪...

当 Ulrich 了解到纳米医生（NanoDoctors）--一种被设计用来治疗疾病的小型机器人--时，他拿着一些凝胶。Odd恶作剧地把凝胶推到 Ulrich 的脸上，几分钟后，Ulrich 突然晕倒并失去了记忆。奇怪的是，失忆症传遍了整个学校，Jeremie 和Odd认为是 Xana 在作怪...

En utilisant un nouvel appareil du laboratoire du collège, XANA parvient à créer des nanovirus, de minuscules machines capables d'attaquer la mémoire du cerveau humain.

Ulrich viene infettato con un nanovirus sviluppato da XANA che gli provoca un'amnesia. Sissi tenta di sfruttare la situazione per farlo innamorare di lei; mentre il contagio si diffonde in tutta la scuola, una volta portatolo su Lyoko Jeremy e gli altri sono costretti ad insegnargli tutto da capo.

Ao usar uma nova máquina no laboratório de físico-química da escola, o XANA cria nanovírus na forma de pequenas máquinas capazes de atacar as células da memória.

Utilizando un nuevo dispositivo del laboratorio de la universidad, XANA consigue crear nanovirus, pequeñas máquinas capaces de atacar la memoria del cerebro humano.