The Atomic Skull is dead. When Batman and Superman arrive on the scene of his explosive demise, they discover that this villain-turned-would-be hero was one of many people to be the subject of grisly—and sometimes fatal—experiments. But who is pulling the strings of these bizarre and unnecessary surgeries? Whom will they experiment on next? And what does one of Superman’s oldest foes, the Ultra-Humanite, have to do with this deadly mystery?