Luther.

A British¬†psychological crime drama television series¬†that centres on DCI John Luther (Idris Elba ), a ‘highly talented’ detective working in London to solve a series of high-profile murders. Created by Neil Cross. With Idris Elba, Dermot Crowley, Michael Smiley, Warren Brown.

This first premiered on the BBC in 2010. Brilliant, but terrifying and addictive. All episodes watched, which means I can finally sleep at night without quadruple checking the doors are locked and that there is nobody under the bed!