'Supernatural' Season 13 Episode 18 release date, plot spoilers: Sam and Dean race against time to save Mary and Jack from Apocalypse world

The mood is about to get more serious in the coming episodes of "Supernatural" season 13, as time is running out to save Mary (Samantha Smith) and Jack (Alexander Calvert) from the Apocalypse world. The hit CW series took a fun and quirky turn in the successful "Scoobynatural" episode, but Sam (Jared Padalecki) and Dean (Jensen Ackles) Winchester remain determined to open a rift in the Apocalypse dimension, in the hope to stop global-scale destruction. Episode 18 will also feature the return of Ackles' wife, Danneel Ackles, as Sister Jo.

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According to the official synopsis for "Supernatural" season 13 episode 18, titled "Bring 'em Back Alive," there will be a clear shift in focus in the series as the Winchesters go back to finding a way to reach Jack and Mary in the Apocalypse world.

As the son of Lucifer (Mark Pellegrino), Jack is a crucial part of the story as he might be the only one who can stop his father's onslaught in heaven. Another hellspawn, Asmodeus (Jeffrey Vincent Parise), also aims to recruit Jack to his side for his own gain, and even though Asmodeus intends to kill Lucifer, Sam and Dean would not allow another demon to win the game.

Previously, the fans saw Lucifer convincing Sister Jo to join him in his conquest of heaven. It was revealed that Jo is not just an ordinary faith healer, but an angel as well, and Lucifer believes that she is a worthy addition to his team because of her remarkable powers.

Sister Jo is set to appear once again in "Supernatural" season 13 episode 18, but it looks like she will be another problem for the Winchester brothers to deal with.

Archangel Garbiel (Richard Speight Jr.) will also make a comeback in "Supernatural" season 13 episode 18, much to the surprise of Sam and Castiel (Misha Collins). After escaping from Asmodeus' dungeon, Gabriel might be a big help for the Winchesters in opening a portal to the Apocalypse world, especially that one of the requirements to make a rift is the archangel grace.

Supernatural Season 13 Episode 18 will air on April 12. 8 p.m. EST on The CW.