McConaughey plays "Rust" Cohle, a very intelligent detective that, due to his own ethics, is compelled to ravenously pursue a serial killer even though it brings great danger to his own well being. Rust suffers from depression, insomnia and alcoholism, all of which stem from the untimely death of his young daughter followed by the divorce of his wife. While Rust may be a flawed character who does not believe in or follow the norms of society, he still acts as the moral epicenter of the show.
Harrelson plays a decorated and veteran detective named Marty Hart. Marty has a troubled relationship with himself, his partner, and his family that eventually leads up to many of the troubles within his character. Marty's demons eventually get ahold of him before he turns to alcohol and divorces his wife. While Marty and Rust are partners they do not necessarily get along, this leads them to disagree on much of the morality of humanity and the human existence.
The plot of True Detective jumps between the years 1995, 2002, and 2012 while Marty Hart and Rust Cohle are delivering the tale of a previous homicide investigation that they both worked on. All previous information on the case was tragically lost in hurricane Rita, so the two characters were asked by investigators to recount their professional relationship, separate home relationships, and affiliation with the Dora Lange murder case. We bounce between the past and present while we progressively learn more about our character, the case, and that the perpetrator may still yet be at large.
I would highly recommend that everyone check out True Detective at some point. It is a show that is shot beautifully with an amazingly interesting story. The first time I watched it I was bored during the first episode and gave up on it; however, after I got to the third the show greatly increases in pace. The show is also scheduled to release a second season coming up in June of 2015.