Watching the relationship between John Luther and his wife as well as his wife's lover is one part of the story seen in each episode. The relationship between John and the crazy killer lady from the 1st episode keeps unfolding with unexpected twists.
With episode 3, the killer is quite obvious once he's introduced to the show and is a typical psycho who takes blood from his victims and stores them alive in a chest freezer. It's quite chilling as you watch how he treats his victim.
An important dimension of John's personality comes out in this episode. John is willing to bend the law and cut corners to capture the killer. So although he's a man of justice, its revealed that he goes beyond the law and breaks the law to execute justice in his own way.
A man who captures women as part of a blood ritual and uses their blood to write satanic messages on his victim's walls a decade apart from one another is the next case for Luther who faces a looming suspension in the wake of Alice hiring a gang of hoodlums to rough up Mark and say "John Says Hi" to him so naturally Mark presses charges despite Luther's assertions that he had nothing to do with it and that he has a killer to catch. As Internal Affairs moves to suspend Luther he decides to play fast and loose with the law to bring down the cult leader with the help of DCI Reed even though it may already be too late to save the mother. Wrenching episode that proves how deep Luther is willing to go outside to law to achieve justice.