Idris Elba (Stringer Bell from "The Wire") is Detective John Luther in the Serious Crimes Unit in London, England. The show is kinda like a darker more violent version of Sherlock Holmes.
Each episode has a creepy serial killer or villain he has to stop. One ep had a guy that killed girls, drained their blood, then froze it. The next time he murdered he'd write weird shyt all over the walls in the previous victim's blood. All the villains are really weird and have creepy traits.
There is also a character that has a relationship with Luther that kinda reminds me of the Joker and Batman. Or Clarice and Hannibal Lecter. I won't say who this character is but they're a sociopath, and would definitely fall into the "villain" category, but most of the people Luther faces are worse so he's kinda like
and accepts the character's help.
Anyway, great show. And the last 2 eps of season 1 in particular are
Fred.