Dean enlists Castiel's help to find out what's wrong with Sam, who reveals he can't sleep or feel any emotions except for physical pain. Castiel discovers Sam's soul is missing and when he goes elsewhere to investigate, the Winchesters learn that Samuel is going to hunt down the Alpha vampire. After torturing the Alpha vampire, Crowley appears to reveal that Samuel works for him to collect alpha creatures and he is the one who brought Sam back from Hell. Crowley tells them that he calls the shots and they have no choice but to follow his orders. After the demon leaves, Sam wants to kill Samuel for betraying and lying to them but Dean lets him go. Samuel tells them that he only works to capture creatures but has no intention to harm the brothers. While the brothers have no choice but to follow Crowley's orders, Sam assures Dean that Crowley will get what he deserves when they get the chance.
Source: Wikipedia
Source: Wikipedia