BBC One has released a new trailer for the return of Idris Elba as the tormented DCI John Luther. The two-part fourth series of the British cop drama sees John Luther pulled out of seclusion to help track a cannibalistic serial killer. BBC One kicks off the two-hour special from December 15th while BBC America will air it in full on December 17th. Laura Haddock, John Heffernan, Patrick Malahide, Michael Smiley, Darren Boyd , Rose Leslie and Dermot Crowley all star in the special in which Elba promises we'll see something "definitely traumatic" happens to the character on a part with the loss of both his wife and best friend in the earlier series.