I am going to summerize what has happened so far so those who read my reviews/summaries of recent episodes don't as lost as they are now [after reading Sin City]. Here goes!
Supernatural is show about two brothers, Sam Winchester (Jared Padalecki) and Dean Winchester (Jensen Ackles). It is based on Myths, urban legends and other SCI-FI related topics. It has a good mixture of emotions, comedy, action, suspence, drama and much more! The boys go across the Country (U.S.A.) in Dean's most loved '67 Chevy Impala to hunt evil.
The boys got involved in this before/during the time their mother got brunt and killed by a Yellow Eyed Demon. That time Sam was only 6months. Since then their father, John Winchester (Jeffrey Dean Morgan) has been trying to locate that YED and also killing other evil things along the way. As the boys grew up Dean, being the elder son basically followed in this father's steps and continued their hunting. Sam on the other side left this life and went off to college to study Law.(This is how they're mother was killed by the Demon)
In this season Dean comes to Sam's college dorm to inform Sam that their father is missing and hasn't returned from his last hunt. Af first Sam refuses to go with Dean but later his Girlfriend is killed the same way his mother was and full of anger and broken down he comes along with Dean. Within this season the boys look for clues to finding their father using his Diary which has information on everything he ever hunted and places he went to and so on. They also kill many evil things along the way. Towards the end of this season the boys meet their father and also find a COLT, made by a famous hunter many years ago. This colt can kill ANY evil thing. (As different evils are killed different ways) But this colt, and its bullets kills one and all. In the end of this season the boys caught the Yellow Eyed Demon by after a fight he escapes (as he had hurt the Winchesters quite badly). Then, all Winchesters bloody, but Sammy hurt abit less than the other two drives them to a hospital but along the way they meet a horrible accident by a truck and their Impala is crushed and the Winchesters left in.
In this season the Winchesters are taken to the hospital. And before this we find out that there is only one more bullet left in the Colt. In the hospital Dean is hurt most severely. He is hurt so bad that John sells his soul and trades the Colt with the Yellow Eyed Demon so that Dean could come back in full health. The boys have now lost their father and they sure that the YED is behind this. Soon they are both back on the Road, after Dean repaired his beloved Impala. Dean feels guilty that his father gave his life for him and now has a huge burden his father told him before he died. He said to protect Sam or he'd have to kill him. Sam thinks this means that Sam will become evil and tries his best to stay his sweet and caring self but fears what the YED has in store for him. In the end of the season the YED kidnaps Sam who had gotten pyschic abilities from when YED put demon blood in sam's mouth the day he killed his mother, and also kidnaps other kids like Sam (whom he did the same with when they were young). The others are kept hostage for months which led almost all of them to kill the other but only two survive: Sam and another man. The other man tries to kill Sam and suceeds...making that Man the successor of the YED's plans, which is to lead an army of Demons to take over the world. Dean is devasted at the death of his brother that he goes to the Crossroads and makes a deal with the Crossroads Demon. The Deal was made. Dean now had a year to live and Sam was alive again. Now Sam becomes alive in the end the Man who had killed Sam was carrying on the YED's plans by opening this Door to Hell which was located on Earth. Luckily the Brothers make it in time to kill that man but the Door to Hell still opens and relases hundreds of demons. Luckily they manage to shut the door before anything else escapes. Dean in the end though manages to kill the YED with the remaining one Bullet in the Colt.
In this season the boys also come across a Hunter's Roadhouse but that roadhouse and its members are killed by demons at the end of the season. Only two survivals, Ellen (John's old Friend) who wasn't in the Roadhouse and JO (her daughter who has ran away from home). They also meet another long friend of John's, Bobby, another excellent hunter who helps the boys. Both Ellen and Bobby were present when the door to hell opened. This season ends with giving the message that there is a War coming and they better be ready.
So far in this season we are in the 8th episode. We are introduced to two new characters, Ruby, who is Demon which is trying to help Sam and is apparently "good", and also Bella, who sort of a hunter except she makes money off of supernatural artifacts. Basically what happened in this season so far is that the boys keep coming across major evil things which escaped the night the Devil's Gate (Door to hell) was opened. They're surprised that if they let the "Seven deadly sins out, what else escaped?". With Sam trying to get Dean out of the Deal he made for Sam and Dean with only a year to live and with Ruby the "good-demon(?)" trying to help Sam and Bella who keeps crossing they're paths and of course with what else escaped from the Devils gate, who knows what will happen next!