The British Men of Letters, Jack the nephilim, and Apocalypse World
23 episodes of Supernatural carry this thread, 23h in all — 16 of them are in The Essentials.
Arc membership is derived from each episode's own summary text, gated to the seasons the sources place each arc in. It shows where a thread is foregrounded, not every episode it touches.
In airing order
While Dean brings Mary up to speed on what has happened in the 30 years since she's died, 'Sam faces torture at the hands of the Men of Letters Meanwhile, Crowley tries to track down a weakened Lucifer, who is hopping from body to body.
Lucifer takes a new host body: the President of the United States. The Winchesters are forced to turn to the British Men of Letters for help to remove Lucifer's essence from his new host, but the Secret Service has other ideas.
Mary convinces a Hunter, Wally, to call in Sam, Dean, and Castiel to deal with a demon. However, she soon discovers that the intel the Men of Letters gave her is bad... and they face a new, powerful threat.
Mary brings Sam to a Men of Letters compound to convince him to join their cause. Meanwhile, Fetch approaches Dean and takes a different approach to recruitment.
Mick convinces Sam and Dean to take him on a case involving a werewolf attack. However, they soon discover that the British Man of Letters has an ulterior motive.
Sam and Dean get a lead on Kelly, but Dagon takes steps to prevent her from making contact with the Winchesters. Meanwhile, Lucifer tries to find a way to deactivate Crowley's wards on his host body, and Castiel is MIA.
The Men of Letters send Sam and Dean to investigate the case of a murderous goat man in Wisconsin while they check out the bunker to learn all of the Winchesters' secrets.
As Kelly prepares to give birth to Lucifer's son Jack, the Winchesters team up with two unexpected allies to stop Lucifer.
Lucifer's son Jack escapes and goes out into the world, and Sam and Dean put things on hold to track him down.
Donatello, the newest Prophet of God, senses God's power and comes looking for him. Meanwhile, a Lord of Hell decides to use Jack to unleash the foulest beasts of Hell. In the other universe, Lucifer and Mary meet the angels including the one who killed "his" Lucifer.
After a wraith kills a psychic, Missouri investigates the death of her friend and calls in Dean and Jody. They help track down Missouri's granddaughter, who also has "the gift" and is the wraith's next target. Meanwhile, Sam tries to help Jack develop his powers.
Two people turn up dead, apparently killed by their deceased love ones. Sam convinces Dean to take Jack with them on the case, and they discover that both victims were seeing a grief counsellor, Mia Vallens. Meanwhile, Castiel meets the keeper of the void that he's trapped in.
After the Winchesters find Castiel, they reunite him with Jack. Together, the group goes to Tombstone to check out a case of grave robbing, and Jack makes a serious mistake.
While Lucifer escapes from Michael and proposes an alliance with Castiel, Sam and Dean discover that someone is killing witches and find a familiar face is responsible.
To obtain a tracking spell that can locate Jack, Sam and Dean make a deal with the new king of crossroad demons. If the brothers steal a trunk for the new demon, Barthamus, then he'll give them the spell. However, things don't go quite as planned.
An artist turns up dead, his eyes burned out, and the Winchesters suspect that Jack was responsible. However, they soon discover that Jack is trying to help them by finding a dreamwalker so that he can locate Mary for the brothers.
Donatello translates the spell and Dean and Castiel go to get the ingredients. Meanwhile, Mary and Jack escape Michael's captivity and meet an old friend for the first time.
Sam and Dean get a lead on the last item they need to open the rift: the Seal of Solomon, at a Men of Letters chapterhouse in Rhode Island. They soon discover something else: a woman imprisoned there for over 80 years. Meanwhile, Asmodeus teaches Ketch his place in the demon prince's hierarchy.
Dean and Ketch arrive in the apocalypse world, and Dean sees a familiar face. Meanwhile, Sam and Castiel try to reach Gabriel, while Lucifer grows bored in Heaven.
Sam and Dean track Gabriel to Central City, Colorado, and find him on a trail of vengeance against the god and his sons who he claims betrayed him. Meanwhile, Jack is ready to take on Michael but Mary preaches caution.
When the group discovers that Gabriel's grace isn't sufficient to open the rift, they turn to another source: Lucifer. However, not all of them survive the trip to Jack and Mary's base.
On Apocalypse World, Lucifer tries to bond with his son. Meanwhile, the Winchesters come up with a plan to get the resistance fighters to safety, but first they have to rescue Charlie and Ketch.
Lucifer comes to take Jack on a tour of the universe, but all is not as it seems. Meanwhile, one of the refugees is murdered and the Winchesters try to find the killer.