The film employs techniques of metafictional parody to make overt critical comparisons between 1990s TV detective shows and their 1970s counterparts. The editorial line taken throughout the film presents a very affectionate portrayal of several of these 1970s shows, despite acknowledging their use of styles and methods that had since become somewhat clichéd.
The title parodies the title of the 1988 film, Women on the Verge of a Nervous Breakdown.
As in the previous film, Bonehead and Foyle attach great importance to guns, witty one-liners and self-conscious efforts at looking un-self-consciously good on-screen. They manoeuvre and park their car – a Ford Capri, as used in The Professionals – with almost exclusive use of handbrake turns, and during the film's climax they concentrate on seeking out piles of boxes to drive through or puddles to splash through, in order to make their shots appear more dynamic.
For the second half of the film they again appear without shirts and, finally, without trousers.
George uses London slang extensively, shouts, chain-smokes and insists on calling his commanding officer "guv". His detective methods involve visiting East End "villains' drinkers" in search of information. In common with Bonehead and Foyle he drives and parks his car – a 1970s Ford Granada, as seen in The Sweeney – recklessly.
Shown to be running a 1970s retro clothes shop (Flares 'R' Us), Bentley dresses in red and purple crushed velvet suits that in retrospect appear identical to typical Austin Powers costumes, although that character would only make his film debut four years after Detectives on the Edge of a Nervous Breakdown was first broadcast.
In solving crimes, Bentley prefers to make no visible effort at all, since he anticipates that all the plot devices required to solve the case will arrive by themselves in due course.
In appearance, he is unshaven with untidy shoulder-length hair, but he wears "expensive Armani suits". In action, he is dour, slow-moving and speaks very little, except in nostalgic non-sequiturs about shipbuilding on the Tyne. Upon arrival at all locations he prefers to stand gazing out of an available window. The writers draw attention to the fact that he always sensibly parks and central-locks his Ford Sierra.
The film opens on the studio set of a fictional 1990s TV show, The Gourmet Detective. This is depicted as a crass cross-genre detective/cookery series ("two recipes and one murder per show"), whose lead character (played by Keith Allen) presents his recipe in a style that parodies Keith Floyd. Allen's "on-screen" Gourmet Detective character is the epitome of politically correct "new man" compassion, but the actor "off-screen" is shown to be an obnoxious, drug-taking womaniser. He is subsequently murdered – the second TV detective to be killed in six months – and the rest of the film involves the search for his assassin.
The police commander (played by Jim Carter) is exasperated that the detective assigned to the case, Dave Spanker, has come up with lots of "Northern nostalgia" but no leads. Cheesecloth and the footprint of a 1970s platform shoe are found at the scene, inspiring him to bring in 1970s-style detectives to help solve the crime – initially Bonehead, Foyle and George. When the platform shoe is revealed to be from the early 1970s, Jason Bentley is added to the team, and the commander insists that Bentley's methods alone are to be used ("no guns, no fast cars, no shouting"). Bentley consequently drives the detectives to a random country house, drinks copious claret, smokes endless cigarettes, and predictably gets nowhere with the case. The frustrated detectives have a punch-up while they are – on Bentley's advice – "waiting for a Mini Moke to turn up".
The commander gives the team a dressing-down, and explains that, with the TV-cop-killer still at large, the production of various 1990s TV cop shows is under threat. In order to highlight further the writers' views of contemporary TV detective shows, he lists these as The Dull as Dishwater Detective, Detectives on the Verge of a Nervous Breakdown and The Whistling Detective Who Lives on a Barge. The Dull as Dishwater Detective is apparently in hiatus because "the actor's run abroad, he's scared" – a reference to the real TV series Inspector Morse, whose lead actor John Thaw was making A Year in Provence at this time. Ironically, Thaw had also played Regan in The Sweeney.
Bonehead, Foyle and George insist they be allowed to proceed with the investigation their way, complete with fast cars and guns. The commander reluctantly agrees to give them 48 hours, and they gleefully wheel-spin away to a rendezvous at an East End drinking den. Meanwhile, a sheepish Bentley asks to see the original lab reports.
At the pub, George asks to see his informant, while Bonehead and Foyle order Babychams then storm the toilet cubicles the way they might storm an embassy. However, Bentley provides the breakthrough. He reveals that the forensic report proves the platform shoes were bought in Newcastle upon Tyne. After Spanker confesses that he committed the crimes due to TV ratings pressure, he makes his escape.
There ensues a 1970s-style high-speed car chase involving all but Bentley, based mainly in a large yard where all three cars drive around somewhat pointlessly in circles. The repeated handbrake-turns wreck Foyle's gearbox and, in frustration at missing out on the car chase, Bonehead briefly considers leaving his partner. However, the chase continues on foot into London Docklands, where Spanker takes refuge.
Bonehead and Foyle – as is customary for them – remove their trousers for this final showdown, and then bemoan the Docklands redevelopment that has taken place since the 1970s: "where's all the wasteland and disused factories?". They nevertheless negotiate the area trouserlessly as if it is still full of rusty girders and rubble, to the bemusement of passing city workers.
Meanwhile, George attempts to talk Spanker into a surrender. Spanker complains that, with the increased realism in TV detective shows, he has missed out on the fast cars and the "shoot a man at a hundred yards crap" enjoyed by his 1970s counterparts. To prove the point, he feels no ill effects when George shoots him from this very distance as an apparent 1970s denouement to the scene. However, Bentley now magically appears exactly where the plot requires him to appear, right alongside Spanker. In a typically relaxed and tangential fashion, he manages to capture the detective effortlessly.
George devises a punishment for Spanker far worse than being shot at close range – Spanker will instead be "shot on tape". He has his scruffy hair cut to a regulation police constable's length, in order to take his place as "a faceless copper in uniform - three nights a week". Spanker's suitably TV-based punishment is to become a member of the cast of The Bill.
The film ends on an up-beat note, with Bonehead, Foyle, George, Bentley and the commander all drinking to "the Seventies".