Simplify the following text for a Grade 3 native English-speaking person.
Original: On their way to Mordor , Frodo and Sam capture Gollum , who has been following them from Moria , and force him to guide them to Mordor . Finding Mordor 's main gate impassable , they travel toward a pass known to Gollum .
Simplified: Gollum has to promise to show them the way into Mordor .