DI Chandler’s (Rupert Penry-Jones) career and life have been mapped out for him — first by his high-ranking career police officer father and subsequently by his godfather, Commander Anderson. He is an expert in the politics of policing, but doesn’t really know who he is, what he believes in or what he is passionate about until the end of the first series when he realises that he doesn't actually care anymore about the gaining of rank and realises he is quite happy to remain a simple DI.
In the first season he is thrust into an established squad and given a seemingly interesting case that grows into a career making opportunity and then back into an albatross as the details become bizarre. His direct superior, Commander Anderson who gifted him the position and case, is also a double edged sword and alternates between a caring and semi-helpful role model to Chandler and as a stilted and ineffectual leader who has apparently given up on police work and plays a political game to keep a high status and pay at the apparent expense of his public duty. This proves an anathema to Chandler and only serves to drive him onward in his course of morality and justice.
Early on Chandler enlists the help of Edward Buchan, a Ripperologist, to help predict the course of the case and is indeed proven correct in most cases while earning the ridicule of his team for such unscientific and speculative methods.
Chandler's attempts to modernise and motivate his team are mostly met with contempt and serve to annoy DS Miles who pushes back just as ferociously. Over the course of the season he earns the grudging respect of his team as his theories are proven one-by-one to be correct and their loyalty grows, while still rejecting his orders for a clean office and healthy food.
In the finale Chandler and Miles close in on the suspect and in a dramatic ending Chandler has to choose between closing the case with an arrest or saving the life of Miles.
During season 2 Chandler's OCD slowly becomes more apparent while his relationship with his team has only strengthened. Again he has to fight the sloth and disinterest of his superiors in order to take on another bizarre case, again gifted to him by Commander Anderson as a semi-poison chalice. He now also has a nemesis in the form of DCI Cazenove who is a very calculating officer who has made incredible leaps in crime reduction and a sinister passive-aggressive demeanour. Anderson is revealed to be dedicated to his young DI and actively aids his investigations to stay off the books and willing to support his wild ideas, if only in private, to get the job done.
Chandler works to bring down the crime empire of the two new Kray Twins while also battling the deceptive Cazenove, culminating in a showdown where Cazenove pulls a gun on Chandler when his complicity is revealed.
Season 3 sees the team dealing with 3 sets of cases over 6 episodes and Chandler installing Buchanan as an in-house help, researching historical crimes similar to those investigated, to see if they can be quicker solved with the use of hindsight.
Chandler's OCD is down played at the start of the season as the show takes a more team procedural approach. Towards the seasons end the OCD gets referenced and shown more.
A potential love interest for DI Chandler is introduced in a victim of the latest killer, she was in protective custody until she was killed by an enraged third party. Said love interest gave chandler a rubber band to keep around his wrist (called it a thought stopper), told him that whenever he felt the need to control things, to flick it. Candler is visibly disturbed by her passing.
Chandler is now very much at home with his team but again, at odds with his comfort his OCD is reaching frightening levels and is now apparently hallucinating. During his hand-washing routine he now is hallucinating foul water coming from the taps and dripping water bothers him greatly. He keeps an elastic band on his wrist and snaps it when stressed, especially when it comes to drowning victims. He became disturbed when he saw the state of John Washington and hasn't really recovered since
The flashing cut-aways between scenes, that have been a feature of the series, have increased in their impact with noticeably louder sound and harsher cuts than previous seasons. This seems to be in line with Chandler's increased OCD.
Personality and Traits
From the outset Chandler is portrayed as uptight and highly inexperienced in the daily dirt and realities of front line police work. Thankfully he has enough force of character to express some outlandish ideas and stick with them even in the face of derision and open hostility from his own men.
During the second season he displays even more anxiety under pressure and showing him washing his hands in the office bathroom become a running theme. He often rubs his temples with oil when stressed and will escape to his office, though often leaving the door open. He also lays out items from his pockets in a neat ordered line while at his desk and gathers them up from left to right carefully as he leaves.
By season 3 he is openly shown as Obsessive-compulsive as he switches a light off and on, leaving and returning to start over and unable to break away from the routine when a life is at stake.
In season 4 it appears that his disorder has gotten much worse as during his bathroom/hand-washing routines he now is hallucinating foul water coming from the taps and the sounds of dripping water bother him greatly. He keeps an elastic band on his wrist and snaps it when stressed, especially when it comes to water and drowning victims, but when it snaps he manages to break the cycle.
In the season 4 episode 2 when another victim is found, a woman drowned, Chandler looks shocked and retreats to the bathroom and starts panicking and twanging the elastic band hallucinating dripping sounds again. This is when his elastic band breaks.
In season 4 episode 2, it is revealed that his father died when he was young and his mother went mad trying to contact him
"When my father died, my mother was desperate to contact him. She needed answers I suppose, she did everything she could to try to talk to him; mediums, em-paths, psychics. They all came to the house and they all took her money, went on for years.She drove herself insane trying to find him."
This quote is spoken by DI Chandler to DS Miles when Miles is overcome with fear of the paranormal, Miles replies with:
"I'm sorry, I didn't know that"
DS Miles: Joe! Lovely. Come in. Did you come on your own?
DI Chandler: Yeah. Happy birthday.
DS Miles: Thanks! Well, you could have brought a friend, or a... partner.
DI Chandler: You think I'm gay?
DS Miles: Wouldn't matter if you were.
DI Chandler: I'm not gay.
DS Miles: No. Well, no one is on the Job, obviously. But don't you worry. My boys are above all that.
DI Chandler: I appreciate your openness and inclusiveness...
DS Miles: Come and have a drink, and thanks for the fish food. Very thoughtful.
MI6 agent: I can assure you, nothing sinister is going on. Why are you so paranoid DI Chandler ?
DI Chandler: Don't play mind games with me.
(season 4, episode 2)
DI Chandler: It started when I was ten you know, I missed my fathers memorial service becuase I couldn't stop washing my hands. My mother had to go without me.
DS Miles: Are you ok ?
DI Chandler: My father drowned himself, I tried to save him but .. i um ... pumped his chest.
DS Miles: I'm sorry
DI Chandler: That's why my mother became obsessed with mediums and spirit guides, she just wanted to know why, why he took his own life.
DS Miles: Did she ever find the answer ?
DI Chandler: no, she stopped taking care of everything. So i had to ... I had to keep order, 'cause I didn't want the world to see that our lives had fallen apart.
DS Miles: Look, I get it, I understand, its a compulsion but it's also what makes you a great detective. That obsession with detail, that forensic mind. I don't have it. I have local knowledge, street smarts. I have hunches and 99 percent of them turn out to be wrong. but you have real insight. it's not a disability, it's a gift.
DI Chandler: But I can't, I just, I can't deal with people the way you can.
DS Miles: Fine, that's what makes us a great team. Maybe they should put your brain in my body ... Mind you then you really would have something to get OCD about. I'm gonna wait outside. and hey (points to a sign in the bathroom that says "Don't forget to wash your hands".
(Season 4, episode 4)