The boys arrive in Chicago to investigate recent violent deaths. Disguised as operators from a security alarm company, they visit the apartment of the last victim. Dean notices that the blood spatter on the carpet forms a symbol.

That night they visit the bar where Meredith worked. Sam spots a familiar face; Meg, the girl he met when he was going to travel to California to find John. Sam tracks Meg to an abandoned warehouse, where he observes her at an altar, communicating with someone through a goblet of blood. Dean calls John and asks him to come to Chicago. 

At the abandoned warehouse, the boys’ plans are thwarted when Meg commands to daeveas to attack them. Once they are restrained, bound to pylons, Meg reveals the murders were a plan to trap them, and use them as bait for John. Sam cuts himself loose and overpowers Meg and then overturns the altar. Freed from her control the daevas turn on Meg, and throw her from the window. Sam and Dean see her dead on the pavement beneath.

Returning to their room, Sam and Dean find an unexpected visitor – John. Their reunion is interrupted when the daevas attack them, but Sam repels them by lighting flares. As they go their separate ways, they are observed by a figure in the shadows – Meg.

A group of teenagers in Richardson, Texas, visit a reputedly haunted house,they find the body of a girl hanging in the cellar. However, by the time the police arrive, the body is missing.Sam and Dean, who are engaged in a prank war, decide to investigate and track down Craig Thursten, who relates the legend, of Mordechai Murdoch, a farmer who lived in the house during the 1930s, and who killed his daughters, hanging them in the cellar.

Sam and Dean visit the house, which has symbols painted from many different origins freshly painted on the walls and floor. While searching the house, the boys run into Ed Zeddmore and Harry Spengler, paranormal investigators, who run a website called Hell Hound's Lair. Mordechai chases them from the house and is not slowed by a blast of rock-salt. Dean and Sam return to visit Craig. Craig admits that he and his cousin painted the symbols and spread the rumour about Mordecai as a prank. Sam postulates that Mordecai is a Tulpa – the manifestation of a thought. One of the symbols painted in the house is Tibetan spirit sigil, which assists in concentrating mental energy. In order to “kill off” Mordechai, the boys tell Ed and Harry that they have found out that being shot with iron rounds will kill him. They wait for the boys to post it on their website, and enough people view it so that it becomes real. Ed and Harry tell them the server crashed, so the new legend will not manifest. As Mordechai attacks them, Dean sets the house on fire, figuring that without that part of the legend Mordechai won’t exist.

In Fitchburg, Wisconsin children in the town are becoming mysteriously ill. Dr Hydeker at the local hospital indicates that no treatments are proving effective with the children, who seem to have compromised immune systems.At the home of the latest victim, the boys find an inhuman handprint on the window ledge outside the child’s bedroom. After checking into a motel run by a woman with two young sons, Michael and Asher, Dean tells Sam he thinks the creature at work is a shtriga, which their father had encountered many years previously. Back at the motel, the youngest child Asher is sick and has been taken to hospital. While Dean drives the mother to the hospital and interviews the doctor again, Sam finds the Shtriga is disguised as Doctor Hydecker - who is working at the hospital in Fitchburg, and is also seen in an 1890s photo.

Dean says John found out they are vulnerable when feeding. Sensing Dean knows more about the shtriga than he has revealed, Sam pushes him. Sixteen or seventeen years ago, John Winchester was hunting a shtriga in Fort Douglas, Wisconsin. While John was out, Dean left Sam alone briefly and the shtriga attacked. John shoots it and takes the boys to stay with Pastor Jim, but when he returned he couldn't track the shtriga. Dean blames himself for its escape, and for the deaths that have occurred since. Dean suggests using Michael as bait to trap the shtriga. Michael at first refuses, but later decides to do it, even though Dean can't guarantee Asher will get better. Dean and Sam set up a system to observe Michael in bed, as they need to wait until the shtriga starts feeding before they can attack. The Shtriga attacks Michael and the boys storm in, only killing the monster when it tries to feed on Sam.After the Shtriga is killed, Asher and the other children recover.

The boys arrive in upstate New York, where Mark and Anne Telesca were found dead in a locked house, the latest in a series of murders over a number of decades in the same area according to research from John’s journal. They visit the Telesca home, but all the furnishings have been taken to an auction house, so they decide to check it out, in case a spirit has itself attached to an object. Sarah Blake, who works at the auction house confirms that the Telesca estate is being auctioned. Before she can tell them anymore, her father asks the boys to leave.

Over dinner, Sarah reveals she hasn’t been on a date since her mother died unexpectedly a year ago.Sarah get’s Sam copies of the provenances of the items of the Telesca house. Dean finds that a portrait of Isaiah Merchant’s family painted in 1910 was also owned by the other families which had been killed. At the local library, they find out that Isaiah Merchant was accused of killing his wife, two sons and adopted daughter. Sam calls Sarah to see if they can view the painting again, only to find it has been sold, to a friend. The boys rush to the house just as Sarah arrives, and they find Evelyn dead, her throat slashed. They examine the painting and more features in the painting have changed, amongst other things there is now a mausoleum in the picture with the name Merchant on it. Sam and Sarah get trapped inside Evelyn’s house, and attacked by the spirit of Melanie Merchant, the adopted daughter. Dean returns to the mausoleum and burns an antique doll which bears some of Melanie Merchant’s hair. This finally dispels her spirit.