3. Alone in the World

Complete story — includes the ending

Two young bullies are found dead and in just a few hours they rot to an advanced state of decomposition. The Fringe team investigates and uncovers a fungus is behind the decay. The fungus is emotionally tied to a young boy, Aaron, who Walter bonds with while having more hallucinations of Peter. He fears he will be considered insane and put back in the mental institution if he tells anyone about them. When the Fringe team discovers the fungus can be killed using ultraviolet light, it becomes clear that due to his emotional connection with the fungus, Aaron would die too. Walter succeeds in severing the connection and the fungus is killed without Aaron being harmed. In the end, Walter finds out that Olivia has similar hallucinations of Peter and concludes that he is not insane.