Simplify the following text for a Grade 6 native English-speaking person.
Original: The Lightning Thief is followed by The Sea of Monsters in which Percy and Annabeth rescue Grover who has been imprisoned by Polyphemus , the Cyclops , and recover the Golden Fleece to save the camp .
Simplified: The Lightning Thief is followed by The Sea of Monsters . There , Percy and Annabeth rescue Grover , who has been taken prisoner by Polyphemus , the Cyclops .