On Supernatural Season 13 Episode 21, Sam, Dean, Castiel and Gabriel get all the things they need for the spell to the other side, but the grace from Gabriel isn't strong enough to keep the portal opened. Castiel comes up with the idea to track down Lucifer because his grace would be strong enough. Gabriel is able to track him down, and with the help of Rowena, they are able to take Lucifer prisoner. 

Lucifer is brought to the bunker, and his grace is drained from him, but he asks why they aren't killing him. Sam let's him know they are going to keep him alive as long as possible because they need to portral to stay opened. The ground, except for Rowena, go through the portal. Lucifer pesters Rowena until she isn't able to take it anymore. She gets angry, and reveals to Lucifer the guys are on the other side because they are trying to save Mary and Jack. Lucifer gets angry and regains his strength. He tries to kill Rowena, but she blasts him into the portal. 

On the other side, the guys are trying decide they need to walk to Dayton to find the camp Jack and Mary are in. As they are walking they encounter a vampire attacking two humans. Sam is able to kill the vampire before he kills the humans. The couple joins the group and heads to Dayton, but they quickly encounter a group of vampires in a tunnel. Sam is killed by the group, but Castiel isn't able to save him because there are too many vampires to battle. 

The group is able to escape, and they soon find themselves in a camp which is surrounded by strong warding. Gabriel destroys the warding, but they quickly realize it's the camp which belongs to Mary. Mary and Dean reunite, but Dean can't get out what happened to Sam. 

Meanwhile, Lucifer finds his way to Sam's body, and brings him back to life. Sam comes too, but wants to know why Lucifer saved him. Lucifer lets him know they need each other to find the camp. Lucifer gives him the option of going with him or staying behind to be eaten by the group of vampires who are still in the tunnel. Sam agrees to go along, and he soon reunites with his family in the camp, but Lucifer is right behind him. 

Make sure you catch up on the entire season before the finale. Go watch Supernatural online now via TV Fanatic.