Simplify the following text for a Grade 4 native English-speaking person.
Original: Odd Della Robbia , Ulrich Stern , and Yumi Ishiyama become involved in these attacks , and Jeremy has no choice but to share his secret with them . Odd , Ulrich and Yumi are sent into Lyoko using 10 f scanners to stop the force attacking their world .
Simplified: Aelita , Ulrich , Yumi and Odd go into the world called Lyoko .