|Sitting in her house, flicking through the TV channels, prostitute Gloria Sitnick comes across a program with an Evangelist talking. No matter what she does though, the TV will not change channel or switch off. Suddenly, she encounters a shining bright light in her house. In a secure hospital, Sam sneaks in, posing as a doctor, and talks to her about what happened night. She claims that an angel came to her and told her to kill a man who was doing something evil. She followed the "word of God" and stabbed a man to death. Now she is completely at peace and happily sits in her locked room all day reading the bible.
Dean, meanwhile, is on lockdown in their motel room after the recent "bank robbery". When Sam gets back, they discuss what they know of the case so far. Dean insists that there is no such thing as angels - he only believes in what he can see. They head out to check the house of the man Gloria killed. He was supposedly good man - a librarian and a church goer but deep in the cellar they find a dead body buried there.
Another man, Zack Smith, drunk and depressed in a dingy room, is suddenly startled by the appearance of a glowing white light, the same as Gloria saw. He goes outside and sees another glowing figure outside a house - a sign that this is where evil lives. He knocks on the door and when the homeowner answers, he introduces himself and then stabs the other man. Dean and Sam both do some more resarch. They discover that the man Gloria killed was probably responsible for several missing students in the past year and Dean hears on the police radio about the murder Zack has committed. They go over to the man's house to look for any evidence of "wrongdoing". Sam hacks his computer and finds a series of emails between the man and a 13 year old girl - including some indicating that he was planning on meeting her. Sam is convinced that this is some kind of avenging angel, but Dean is still sceptical. They find out that the two victims were both members of the same church, so they decide to dig a little deeper. They learn from Father Reynolds of the church that some angels were in fact killers and warriors - not the pretty picture they are usually made out to be. On the way out, they find out that Father Gregory was shot outside the church and killed on the doorstep. Dean is sure that the "angel" is actually the spirit of the murdered priest, but Sam still argues, revealing to Dean that he prays every day.
They check out Father Gregory's grave and while there, Sam sees a statue of an angel move and the same bright light that the others saw. He is even more convinced than ever that he saw an angel and that he was given a mission to stop a man who is going to do something bad. Dean tells Sam that he must have inherited his faith from their mother - she used to tell Dean every night that angels were watching over him. But, he argues, her faith didn't save her. He still insists that this is a spirit. They decide to summon Father Gregory's spirit using a seance ritual in John's journal. If it is the spirit causing the killings, they can put him to rest. If it's an angel, nothing will happen. While getting the things they need for the ritual, Sam sees his sign - he knows who he has to stop. Reluctantly, Dean follows the man, ensuring that Sam wont have to kill, and sends Sam back to perform the seance. Sam performs the ritual but is interrupted by Father Reynolds. Despite the interruption, the spirit of Father Gregory is summoned, stating that he has come in repsonse to Father Reynolds prayers. Father Gregory believes that he is an angel, sent to do good - he thinks he is carrying out God's will, but Father Reynolds is quick to point out that he is simply murdering people.
Meanwhile, Dean has followed the man and found him about to rape a girl in his car. Dean saves the girl, but the man drives off - with Dean giving chase.
Back in the crypt, Father Reynolds finally gives his friend Last Rites, allowing his spirit to be at rest.
Dean continues chasing the would-be rapist, narrowly avoiding crashing his car, but the other man is not so lucky - he collides with another car at a junction and ends up with a steel pole in his chest. Dean recalls an image he saw at the church of the Archangel Michael who used a steel sword to destroy demons.
Later, Sam reveals to Dean that the reason he wanted to believe so much is that he hopes that some higher power will be able to save him from turning evil.