When the Winchester brothers encounter a certain time lord and a consulting detective, they learn the truths of the angels, where they go when they get taken by the empty, and what they turn into.
This story is based after Castiel got taken by the empty, and Dean has to come to terms with his feelings for a certain fallen angel.
I'm not including what happened in 15x20.
What will the Winchesters do when they find themselves in a place they never thought they would be...the Empty.