After passing the scene of a recent murder Buchan turned up at the police station claiming to know all about the murder. In an interview with Chandler and Miles he prefectly describes the murder, complete with unreleased details, but is thrown out by Miles when he reveals his profession and that his description was of the first offical Ripper murder.
Chandler keeps a copy of Buchan's book and attends one of his tours and takes advice on a possible scenario for the next murder. When it occurs Buchan becomes both a resource and a suspect. Chandler identifies that Buchan might be simply in tune with the murderer's ideas or even a rolemodel (his theories appear to be those of the murderer as to what was ripper canon and what the ripper's intentions were). Miles is far more secptical and believes him either a hinderance or the perpetrator.
As the season ends the killer is revealed to be a fan of Buchan and even uses him to enable one of the harder to achieve murders, much to Buchan's distress.
With the next case it is revealed that Buchan had previously made a low budged video series on the Kray's and is used by the team to get background information on their crimes and used his contacts with their associates to predict potential crimes.
Towards the seasons end he steals and item with Kray DNA on it to help prove the linage of the new Kray's.
Installed as an in-house researcher in the basement Buchan has a fulltime job researching historical crimes releated to those under investigation with the hopes that they can shed light and hasten results. Meg often helps him with information gathering and seems to be the only team member to show him much respect.
In the latter part of the season the cumalative effects of the murder researching (specifically the murders he fails to prevent) start to weigh on him heavily. He seeks out professional help to help deal with his percieved failures.
In much the same role as season 3 Buchan is again researching older crimes to predict how the current crime might be solved.
His psychosis also increases as the sight of mold on the basement wall sends him into terrified hysterics as he beleives that it will destroy all his resources and cripple his ability to solve crimes.
Personality and Traits.
An apparently bold and self assured novelist Buchan is revealed to be a dedicated biographer of Jack the Ripper, using his detective work to expand and refine Ripper-law. He fancies himself as an amateur detective and often butts heads with DS Miles over his abilities and lack of training.
As he intergrates with the team the toll on him for the murders he fails to prevent (those between the time the case starts and when he finds some evidence to help bring down the killer) weigh on him heavily until he has to seek professional help.
His over inflated sense of self importance in the team irritates Miles in particular.