Complex sentence: Ernest remains determined to look after his son without outside interference but when the Ms. Kemp threatens to take Toby away Ernest persuades his son to demonstrate his ability by summoning items from a picture book.
Split into simpler sentences: Ernest remains determined to look after his son without outside interference. When the social worker comes calling and threatens to take Toby away, Ernest persuades Toby to demonstrate his ability to her, by summoning items from a picture book.