Ghost Channel

S1, E24: On this day, as on many others, our heroes have successfully deactivated a tower. As usual, they are sent back in time, but this time, when Jeremy arrives in Mrs. Hertz science class twelve hours earlier, he realises that Odd, Yumi and Ulrich are not there. They have not "come back" from Lyokô. In a panic, Jeremy starts an inquiry and quickly discovers that his friends’ absence is due to one of Xana’s evil plans.