Complex sentence: A lonely and vulnerable Sarah talks to Gary on the internet and unwisely arranges to meet him at his home in the impression that he is a 19 year old boy, but was surprised to see an older man open the door.
Split into simpler sentences: A lonely and vulnerable Sarah talks to Gary on the internet. Sarah goes to his house; under the impression that he is a 19 year old boy, but was surprised to see an older man open the door.