Complex sentence: Batman is frustrated at his inability to explain himself to Dredd, until telepath Judge Anderson scans Batman's mind to ensure that Death is not "hiding" in his brain, and explains Death's nature and motives to Batman.
Split into simpler sentences: Batman is frustrated as his inability to explain himself to Dredd, and telepath Judge Anderson enters. She scans Batman's mind to ensure that Death is not "hiding" in his brain, and explains Death's nature and motives to Batman.