It's all going to come crashing down on Dexter and Deb in this 8th and final season of the series. When we last left off, Deb had murdered LaGuerta in the shipping trailer after discovering that Dexter was about to do the deed himself. That was pretty much the moment when the sh*t hit the fan.
In the trailer for the new season, we witness the aftermath and Dexter's attempt to not so much pick up the pieces, but come to terms with what he's done. Debra has basically withdrawn completely from her job and Dexter, and appears to be coping with what she's done by loading up on prescription pills and sleeping with a criminal of some sort.
In the standard fashion of the show, there's a new character that presents a problem for Dexter, this time a criminal psychologist who's devoted her life to the psychopathic mind and is now working with the Miami PD.
The trailer does its job of building anticipation for the June 30th premiere, without presenting all too obvious spoilers.