EW's Inside TV reports that Dean will be helping others and keeping secrets in the vampire-centric episode:
Dean is called to aid the being that helped him out of Purgatory (but can’t tell Sam!) and Sam, meanwhile, spends some time with the lady friend he fell for while apart from Dean.
Said being sounds like Benny, the bad vamp Dean is stuck with being indebted to after their escape, and Sam's lady love would be Amelia, the vet we will meet earlier in Season 8 (read more about them here and here).
We'll meet Andrea -- a wealthy, well-bred woman who is anxious to restore her romance with a former flame. As can be expected on this show, though, Andrea's got some secrets up her sleeve.
We'll meet another "age-old vampire of unspeakable evil" -- whose dark, horrifying nature and ancient anger is hidden by his youthful, innocent appearance.
We still have a bit of a wait to meet everyone, though, as Season 8 of Supernatural doesn't start until October 3. Until then, stay tuned here for more spoilers!