Complex sentence: Grant's sister Kim arrives in town to stay with him and he concerned when he learns Kim has not told their parents where she is but remains unaware that she has a drug habit until after Steven Matheson (Adam Willits) and Matt find out.
Split into simpler sentences: Grant's sister Kim arrives in town to stay with him and he is concerned when he learns that Kim has not told their parents where she is. He remains unaware that she has a drug habit until after Steven Matheson (Adam Willits) and Matt find out.