As we know Cas, he won't do such thing as letting Lucifer take control of his body during the episode, "The Devil in the Details." But it's like he made the decision for the greater good.
Cas previously went to the bad side when Leviathan was the foe that they need to kill. But we will understand and will be able to accept what he did if we'll going to watch the 14th episode of the series, "The Vessel."
There is no need to have to wait any longer for Dean and Sam to know who is inside Cas. As per Collider, it is horrible when cast members keep the audience waiting.
During the episode, Sam Winchester is trying to find a way to defeat Amara or "The Darkness." And it led to an object that was lost during WWII in a US submarine.
The object that they need to retrieve is the Hand of God. Knowing that it was lost in 1943, Dean plans to time travel and was able to get it.
A report from Popmatters, enthusiasts knows that angels have the power to time travel. And the brothers called Cas to send Dean back to 1943 and that's the time where Dean found himself on a submarine.
The captain of the submarine didn't have faith on Dean since then. And others was not able to grasp the saying about the device that he has called cellphone or even about baseball knowledge.
Member of Men Of Letters and French Resistance, Delphine, played by Weronkia Rosati, is the only one who trusts him. And she is carrying the Hand of God, but there is a sign in her chest that links her to the item.
Meanwhile, Lucifer is ruling hell while playing a game and inflicting pain to Crowley. And he didn't want to pretend anymore and told Sam the truth.
Lucifer was planning to use the soul of Sam to go back in time and get the Hand of God. But Cas was able to overthrow Lucifer.
When Dean came back from the past, Sam gave him an idea what has happened. And Sam expels Lucifer away with the ritual however, they find that the power of the Hand of God has been depleted.
Now, they need to find another way to win against the Darkness. In spite of what happened, the episode was able to portray what will happen next.
