Fairbank was a close friend of Ted Hastings, with the two having met during his police career and belonging to the same masonic organisation. Fairbank is a paedophile, having used his position of power to sexually abuse young boys at Sands View.
In the 1990s, Fairbank was the leader of the Vice Squad of Central Police. At some point in his career he became corrupt and entered the criminal underworld. Utilising his position as a police officer, he was able to not only take part in sexual abuse of children in the Sands View Boys Home, but also cover it up.
Whilst looking into the disappearance and death of Oliver Stephens-Lloyd, DS Steve Arnott and DC Kate Fleming grow curious as to why Fairbank was included on the distribution list of the missing persons report, as he was in charge of a completely separate department at the time.
Wendy Rider is visited by DS Steve Arnott and DC Kate Fleming regarding a complaint she filed against Chief Superintendent Patrick Fairbank. The complaint was that he had failed to investigate allegations made about former Councillor Dale Roach in regards to her son Gregory Rider.
After Joe Nash identifies Fairbank as one of the abusers in an identity parade, he is brought in for further questioning. Despite maintaining his ignorance, Superintendent Ted Hastings sees through the facade and has him arrested for sexual activity with a child, perverting the course of justice and misconduct in public office.
Later in the episode, Gill Biggeloe confronts Hastings and announces that Fairbank's legal team are petitioning to have the charges dropped, as Fairbank's GP has testified that he has early onset dementia and thus will be unable to stand trial. She claims that AC-12 should have examined his mental state prior to questioning him, as he did repeatedly state "I'm not as sharp as I once was".
During AC-12's inquiry into Operation Lighthouse DI Steve Arnott discovers Gail Vella was investigating the murder of Lawrence Christopher around the time of her death. The Senior Investigating Officer on the botched enquiry was Marcus Thurwell, who worked under Fairbank. In the time since series 3, Fairbank has been moved from HMP Blackthorn to an open prison due to his deteriorating health. Steve Arnott and Chloe Bishop go to HMP Queen's Chase to question Fairbank on his links to Thurwell. However, Fairbank's poor mental state, lack of recollection and apparent incontinence, leads to a visibly-frustrated Steve and Chloe having to cease their questioning of Fairbank, their visit proving fruitless.
After an attempt by the OCG to kidnap her during a prison transport from HMP Brentiss, DCI Joanne Davidson reveals that she believed Fairbank to be her biological father, and was taught to fear him by her uncle Tommy Hunter.
Suspecting Fairbank is the Fourth Man, AC-12 authorise a search of his prison cell in search of the laptop known to be used by H to communicate with corrupt officers and the OCG. However, the search returns nothing suspicious. Nevertheless, AC-12 question Fairbank on his involvement in the murders of Gail Vella, Jimmy Lakewell, John Corbett and others. Fairbank denies any recollection of the individuals mentioned, an assertion that is likely true given the communications are later found to have come from DSU Ian Buckells. Fairbank is then questioned on his relationship to Joanne Davidson and her mother Samantha Davidson. Again, Fairbank denies any knowledge, claiming as usual that he is not as sharp as he used to be, and that AC-12 are "going back years"