Dean went hunting with Sam. After they got back to Bobby's house, Sam had to rest. He was injured by a werewolf they suddenly encountered. Bobby takes care of him while Dean is in the kitchen, looking in his laptop, for new strange activity in the area.

You and the Winchesters aren't really friends - no better said than enemies. Your families have often been competitive over the years, not really working and helping each other since Dean can think. After a while, before you turned 16, your family moved their "home" to another state.

After a few years you came back to Kansas. Bobby heard about you and called you to see if you would help him with a case. You said yes, after all, your family had always been friends of Bobby's. Unfortunately, you didn't know that Bobby wanted you to help Dean while Sam was recovering.

You are on your way to Bobby's house. When you reach it and see a black Impala parked in front of it, you immediately get a bad feeling - but hey! - you decide to push it away. You've always been good at overthinking things. You reach the door and knock.