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|Crowley approaches Dean and Sam telling them he has a job. Initially Dean is "reluctant" (read confrontational). Crowley points out that he can send Sam back to hell at any time. Crowley then sweetens the pot by offering a deal: Bring him an Alpha, and Crowley will give Sam back his soul. Reluctantly, they agree given what's on the table.
Crowley sends Dean and Sam to Buffalo, New York to investigate what appears to be a werewolf attack. When they arrive, they learn about another attack. Both men had their chests ripped open and their hearts missing. Sam whips out the trusty laptop and discovers the link. Both men had threatened Cal Garrigon. The brothers follow Cal, waiting for him to turn into a werewolf, but an entire night passes without him changing.
Then, Cal is murdered with the same modus operandi. The boys focus on the next most likely werewolf, Cal's girlfriend, Mandy. Sam, being soulless and all, is ready to take her to Crowley. Dean wants more proof first, however.Dean goes to the crime scene where Cal was killed to investigate further. Meanwhile Sam watches Mandy to see if she changes. Dean's investigation turns up no new clues. However, Sam sees the family dog, Lucky, change into a man, put on clothes, and leave the house.
Sam follows Lucky to the park where he speaks to another man. Sam tries to get closer, but "Lucky" smells him, turns back into a dog and runs. Sam pursues, but Lucky is hit by a car. The driver of the car, quickly "rescues" Lucky and puts him in the back seat to take to an animal shelter. Sam talks to Bobby and finds out that Lucky is a skinwalker. Sam calls Dean and relays the information.
The brothers retrieve Lucky from the animal shelter, binding him in rope and silver chains to restrain him. The man posing as Lucky tells his story: He was homeless and destitute when he was approached and recruited to become a skinwalker. He was told that allowing himself to be turned would make him strong and fast.
Lucky reveals that the pack consists of around thirty skinwalkers who have been recruited and are living with families as pets. Once they are given the sign by the pack leader, they will infect their adopted families, increasing the size of the pack exponentially. Lucky says that there are skinwalker packs in many towns, but he knows nothing of the Alpha skinwalker.
Lucky takes them to the pack leader, but the pack leader, suspecting Lucky has already kidnapped Mandy and her son. He holds them hostage, threatening to kill them unless Lucky turns them. Sam and Dean star shooting with silver bullets, killing all the skinwalkers. Lucky is shot, but, though wounded, manages to escape.
Lucky, in human form, goes to visit Mandy and tells her how he appreciated her kindness, but she tells him to leave. Heartbroken, Lucky changes back into a dog and leaves.