Complex sentence: Rumplestiltskin then arrives and tells Emma that he's calling in the favor she owes him: she must leave Storybrooke with him that day to aid him in his search for his son.
Split into simpler sentences: Rumplestiltskin then arrives to inform Emma that he's calling in the favor she owes him. She must leave Storybrooke with him that day to aid him in his search for his son.