“The Vessel” is a very clever title which refers to both a method of transportation and to the body that’s possessed by a demon or angel. This episode involves both.
The episode opens in Nazi occupied France. A Nazi general shows his French lover, Delphine (Weronika Rosati, “Strazacy”), the secret weapon which he plans to use against Germany’s enemies. She stabs him in the neck with a hair pin and runs with it. The Men of Letters weren’t just American, or men.
Meanwhile, Sam (Jared Padalecki, “Gilmore Girls”) has been trolling through the Men of Letter’s archive and discovers a record of the Nazi’s lost weapon: The Hand of God. He tells Dean (Jensen Ackles, “Smallville”) that it was an artifact said to have been touched by God and containing immense power. Sam uses a super fancy scanner, which I can only assume Sam stole, to translate a French record to discover that the submarine transporting the Hand of God was lost on its way to the Bunker.
Lucifer (Misha Collins, “24”), still wearing Cas as a vessel, has taken over Crowley’s (Mark Sheppard, “White Collar”) position as King of Hell and his lack of interest in the daily affairs of Hell is upsetting the demons. One demon steps up to try to convince Lucifer to do something, anything, when Crowley grunts in complaint from the corner where he is being held prisoner. He berates the demon for disrespecting Lucifer, playing the role of “good doggie.” When questioned by Lucifer he admits that he believes Lucifer isn’t strong enough to beat Amara (Emily Swallow, “The Mentalist”). Lucifer admits that it may be more of a team effort than he let on, and then, speaking of the team, Dean calls Cas’s cell phone.
Lucifer visits them at the bunker, playing the role of Cas, to tell them that he believes the Hand of God will be the perfect weapon against Amara and that he can get them on to the Submarine. Sam is puzzled because as far as he and Dean know Cas can’t even teleport. Lucifer ad libs by telling him that time travel is a whole different system. Dean volunteers to go because he believes that Sam is the only one who can kill Amara and needs to stay alive if things go wrong. Lucifer agrees to stay by Dean’s side, but when Dean lands on the sub he is alone. Dean hides and notices a warding symbol; Delphine is pulling out all the stops.
Back at the Bunker an upset and soaking wet Lucifer returns admitting that he couldn’t make it past the hull. Sam tries to get Cas to send him in after Dean but Lucifer berates him for bad ideas. He then complains about losing the weapon but quickly corrects “it” to “Dean” when Sam gives him a suspicious look. So Sam goes looking for a way to break through the wards.
Dean “borrows” a uniform from a sailor, Petey (Grant Harvey, “The Secret Life of the American Teenager”), and tracks down Delphine but almost blows his cover when he uses the wrong slang. When he reaches her, she attacks him and he barely has time to drop the phrase “Man of Letters” before the sailor whose clothes he borrowed and the Captain (Darren Dolyniski, “The Man in the High Castle”) nab him. They search him and find his iPhone, so Dean decides to go for it. He admits he is on a mission from the future and informs the Captain that within the hour his Submarine will go down.
Despite the fact the radar has picked up a surface ship heading straight for them, the Captain doesn’t believe Dean and leaves him under guard. Dean asks Delphine about the warding, admitting to her that his ride out of the past is being blocked by it, while he fends off questions from Petey about the future (I wouldn’t know who won the World Series back then either). He explains that the submarine is going down either way, the only difference is whether the Hand of God goes down with it. He promised that they will win the War, but explains that he is fighting his own war which is just as big, if in a different way. Delphine agrees to help and goes to remove the warding. Petey asks Dean how long until they win the war, what the chances of his friends and family surviving, even if he won’t. Dean has to look him in the eye and admit that it will be years still until the war is won.
Sam discovers a spell which can help an angel get past all known forms of blocking, but the problem is that the spell requires an archangel. Luckily, they have one, unluckily, Sam doesn’t know that Cas is Lucifer. Lucifer decides to do the spell anyway.
The submarines sinks lower into a defensive position and arms the torpedoes for battle. But, just as they are about the fire, the German ship vanishes from radar. The Nazi’s have some tricks of their own. When it reappears it’s right on top of them. Delphine returns with just one warding symbol left: her. She is a part of the spell and Dean must kill her in order to break the warding. Naturally Dean is reluctant. And then the sub is hit by a depth charge.
Sam discovers that Lucifer is doing the spell anyway and it worried that it will hurt Cas to do the spell so he offers to let Cas (Lucifer) touch his soul. By touching a soul an angel can gain more power, but it is almost very dangerous for the owner of the soul. Sam trusts Cas, but Cas isn’t home. The irony of Sam telling Lucifer that he trusts him causes him to break character. He laughs, asking himself out loud why he is trying to spare Sam when Dean is the one with the connection to Amara. He compares Sam to the girl that keeps turning him down at Prom. He pins Sam to the wall and tells him that he will tell Dean Sam’s death was an accident caused by him using Sam’s soul for the spell. But, when Lucifer sticks his hand in Sam’s chest, Cas fights back.
Cas is able to talk to Sam for a bit while he fights for control. He admits that he chose to let Lucifer in because he believes Lucifer will be more useful in the fight against Amara. Besides, now he cannot eject Lucifer because Cas can’t get to Dean without Lucifer’s power.
The Germans send a message to the submarine in an attempt to get Delphine to turn over the Hand of God. The men refuse to give in to Nazi demands and Delphine decides to use the Hand of God to destroy the German ship. The power of the Hand of God consumes her and in the process destroys the warding tied to her body allowing Lucifer to retrieve Dean.
The two land back in the present day, but the cat’s out of the bag. Lucifer throws Dean across the room and monologues about how hard it was to play Cas. While he rants, Sam draws an angel banishing sigil. Lucifer attempts to use the Hand of God only to discover that its power is all used up. Then he’s sent away by Sam’s sigil.
The episode ends with the two brothers sitting on a dock talking it out. Dean says that there isn’t any other course of action besides the obvious. They stop Lucifer and save Cas. Dean refuses to believe that Cas chose to let Lucifer in willingly. Then the conversation turns to Dean’s time on the submarine. He admits that he did nothing. He was just a witness to the real heroes. The scene ends with a pull out shot to the tune of Edith Piaf’s “Non, Je Ne Regrette Rien,” ironic considering that Dean probably regrets many things.