Supernatural 'First Born' Review: Dean and Crowley meet Cain, while Castiel and Sam look for Gadreel

After last week's strong installment, Supernatural continued its Season 9 momentum with "First Born," an episode that somehow managed to add a whole new layer to the mythology of the show, which is an impressive feat after eight-plus seasons.

Dean and Crowley went on a hunt together to locate The First Blade, the only weapon capable of killing Abaddon. Their search led them to Cain, as in Cain and Abel. The first murderer turned out to be a demon, but he was retired. Eventually, we learned that Cain carries a mark that allows him to wield the blade, and he transferred that mark to Dean.

Supernatural continues to find ways to branch out its mythology, which has been well established into the ninth season. We learned seasons ago that Dean and Sam's bloodline stretches all the way back to Cain and Abel, so it was great to see the two finally interact. It seems too clean that Dean could just take this mark from Cain without any consequences (Cain even said as much), so expect some nefarious side effects as the season progresses.

Sure, Crowley was playing Dean the entire time because he knew he needed Dean to wield the blade, but the reluctant partners really seemed like they were in a buddy cop movie for much of the episode.

Elsewhere, Castiel discovered that Sam had some of Gadreel's grace left inside of him, so they decided to use it to try and find the angel. Unfortunately, this required the insertion of an extremely large needle into Sam's neck to extract the grace, and the process nearly killed him. But thanks to Castiel's experience as a human, he was able to empathize with Sam and stopped before anything fatal occurred.

The two strongest aspects of the episode were the unique pairings and the exploration of the lingering effects of Cas' humanity. Dean and Cas have spent plenty of screen time together over the years, but Sam and Cas rarely interact one-on-one. This episode offered a chance for the two to strengthen their relationship, and the two took major steps forward by the end of the hour.

Former Human Cas is also proving to be an incredibly deep character, and Misha Collins is playing him expertly by walking the line between angelic robot and human-in-training. It's clear that Cas' experiences from the first half of the season will inform his decisions going forward, and stopping Sam's pain was hopefully the first of many such examples to come.

Notes from Dad's Journal:

-       The references to John Winchester this late in the game are always welcome because they remind us just how far the Winchesters, specifically Dean, have come. Plus, they tie the latter seasons to the earlier ones.

-       Another person (Tara) dies indirectly because of Dean, who was already getting hammered at the beginning of the episode. This is going to get worse before it gets better.

-       Castiel can't enjoy a peanut butter and jelly sandwich. Poor guy.

-       Also, Castiel dropped this little gem when Sam accused him of being a terrible liar: "That's not true! I once deceived both you and your brother!"

-       Cain's backstory was more complicated than previously assumed. It turns out he sent his brother to Heaven, while Lucifer earmarked him for Hell. He then created the Knights of Hell, only to retire when he met the love of his life, Collette. Unfortunately, he accidentally stabbed her to death with the First Blade just after Abaddon, who was trying to coax him out of retirement, left her body. No wonder this guy put himself into isolation.

-       Castiel told Sam and Crowley told Dean that they're going to need all the help they can get with the Gadreel and Abaddon problems, respectively. Maybe this is what brings the Winchester brothers back together?

What did you think of the episode? Let us know in the comments below.