The mid-season hiatus of "Supernatural" Season 11 will end with the premiere of Episode 10 "The Devil in the Details" on Wednesday, 20 January. In the episode, a lot of the questions fans had regarding the return of Lucifer (Mark Pellegrino) will be answered.
In the mid-season finale episode, Sam (Jared Padalecki), with the help of Crowley (Mark Sheppard) and his mother Rowena (Ruth Connell), had visited Lucifer in his cage. While Sam had assumed Lucifer is the answer to defeat Darkness (Emily Swallow) because of the visions of the cage that he assumed God sent him, Lucifer reveals that it was he that one that sent the visions.
The arrival of Darkness on Earth apparently caused his cage to crack, allowing Lucifer to use his powers on Sam. He made Sam see the vision of his cage, and tricked him to come down. Once the fallen angel got the younger Winchester in talking distance, he revealed that he could defeat Amara aka Darkness, but he will need Sam's "meat suit" in return.
However, when Sam refuses, he traps Sam in the cage, and is most possibly getting ready to re-start the torture, when the episode ended. In promo photos from the upcoming episode Dean (Jensen Ackles) and Sam are seen in the cage along with Lucifer, and it looks like Dean may be trying to take on the Devil.
From a recent trailer for the rest of the season, however, it looks like Lucifer has found a way to enter Cas' body. In one scene the words "I Am Coming" is seen carved on Cas' chest, while another shot shows him about to make out with Rowena. Considering Rowena has a huge crush on the Devil, it is highly likely that it is Lucifer possessing Castiel's body that is getting romantic with Rowena.
Watch out for Season 11 Episode 10 of "Supernatural", which will be aired at 9pm (EST) on Wednesday, 20 January. You can also live stream "The Devil in the Details" via The CW website.