In 1929 a priest and author, Ronald Knox, laid down a set of rules that have come to be known as the Ten Commandments of Detective Fiction. They cover the use of everything from secret passages to identical twins, but the first rule is simple: the criminal must be mentioned early on in the story, and not introduced as a final act twist. With Knox’s rules in mind, the third episode of Trigger Pointcould be neatly summarised as a man-by-man run-through of all the characters who, however implausibly, could turn out to be our psychotic bomber. Which, with Trigger Point, is about every other character.

The previous episode ended with Vicky McClure’s Lana “Wash” Washington, scalpel in hand, breathing heavily in the direction of a new bomb, this time planted in a mosque. If the suspense has been killing you for the past week, the resolution comes quickly: Lana, thanks to the intervention of her colleague Danny (Eric Shango), bottles it. Before the opening credits have even rolled, she’s sprinting out of the building, leaving the minaret to be blown to smithereens. The success rate of the ExPo unit so far has left a lot to be desired.

Back at police HQ, the largely interchangeable cast of coppers announce that they’ve received an encrypted message from a group taking credit for the mosque attack. “This is payback for Whitehaven” a robotic voice proclaims from an iPad. “We call on the white race to take up arms, we are the Crusaders!” But the gang aren’t really convinced: they still believe that the Whitehaven estate bombing, which claimed the life of Adrian Lester’s Nut, had the same perpetrators as the mosque attack. White supremacists, they suspect, are trying to stoke racial tensions and confuse the police investigation.

Colonel Mustard, Professor Plum, Reverend Green…

Throughout this, Wash is on edge. She has, after all, recently witnessed at close quarters her colleague and mentor reduced to a heap of limbs, and then, within the space of a really fraught week, almost had her own head forcibly removed. Returning to the ExPo hangout zone, she slams her subordinate John (the one we’re already suspicious of because he’s been peddling the Islamist line, played by Kris Hitchen) against a cop car after he questions her authority, seemingly without fear of repercussion. Perhaps that’s just the workplace culture, or maybe Lana is one of the Met’s “few bad apples” we hear so much about.

John is the first “suspect” to appear in this episode, though he won’t be the last. Next up, Wash is called to a police station to collect her little brother Billy (Ewan Mitchell) who has been involved in an apparently racially-motivated fracas. “A Halal butchers?” she asks him, incredulously. “We’re at war,” he replies. It’s plain to see that Billy is another potential bomber – not least because he’s recently fixed up his car, lives a reclusive vampiric lifestyle, and has presumably picked up some heavy explosive tips from his big sis.

Love in the time of active spree bombing

The third potential bomber to enter the action of this episode is Warren Brown’s Karl, the teetotal ex-squaddie turned car mechanic who was Wash’s knight in shining armour at Nut’s wake. On a whim she decides to visit him at work, where she’s greeted by what I can only describe as one of the largest, most beautiful, dogs I’ve ever seen on television. The chemistry between me and this huge mutt, Nelson, was such that I could barely take in any of the bantering between Wash and Karl, as they bought “Vietnamese weasel coffee” and shared their reflections on the horror of war. “We lose part of ourselves out there,” he confides, “and we never get it back.” The Karl doth protest too much, methinks.

They flirt some more in an almost empty pool hall (and also do some more reminiscing about the times they’ve watched loved ones die, which is a weird kind of foreplay). “I’ve neutralised an IED while the Taliban are taking pot-shots at my head,” Wash tells Karl, while lining up the black, “so I think I’ll be alright.” This is but one of many lines in Trigger Point that are clunkier than a stone age Rube Goldberg machine (or that comparison).

Later that evening, she’s back with lizard/man hybrid DI Youngblood (Mark Stanley). Wash partakes of a joyless Indian takeaway while her nominal boyfriend makes small talk about CCTV, police records and other sexy stuff. As Wash takes in new information about the mosque bombing suspect, a bloke called Nick Roberts who’s doubtless a patsy, Youngblood devours the rest of his curry with the feverish intensity of a man who’s just returned from a long weekend drinking his own urine with Bear Grylls. It’s all in stark contrast to her pool hall larks with Karl, though, frankly, she has bigger fish to fry, and could maybe wait for the spree bomber to be neutralised before getting embroiled in a love triangle.

Youngblood seems to sense that Wash is distracted, and possibly falling for another bloke, because he expedites their relationship, asking her to move in. “I want to protect you,” he tells her; another huge red flag. He then doesn’t even wait for her answer before announcing that “it’s sorted then” and vamoosing her dinner. It’s a shame that she doesn’t manage a proper meal because she’s going to need all her strength the next day when, you guessed it, another bomb is discovered!

Not the dreaded danger zone!

This one is in a van parked outside an LGBT pub called The Five Oaks. It is, the ExPo team assures us, stuffed full of explosives that would tear the entire street apart. The stakes are high: even though the area has been evacuated, ITV simply cannot afford an explosion that size. Wash and Danny bring out the trusty robot, but their attempt at disarming the bomb is complicated when a sniper opens fire. The robot cops a few bullets to the body, and ceases to be able to do its job. This, I suspect, is going to be a trope of the series: something will always go wrong with the useless robot, necessitating a risky but exhilarating manual disarming of the bomb. “Lana, you’re in the danger zone!” Youngblood yells as she approaches the vehicle, a line that, for fans of adult cartoons, was almost certainly said at some point in Archer.

Over in the tower block, Youngblood’s team rather too easily neutralise (a professional euphemism for “shoot in the head”) a man, the aforementioned Nick Roberts, who emerges from a lift wearing a suicide vest. Sadly for fans of simple resolutions or three-episode mini-series, he’s not the gunman. Upstairs, the real sniper expertly cuts the throat of an armed police officer (“His missus is six months pregnant” cliché alert) and then slips out of the building and into a white Toyota Prius (“We’re looking for an Uber in a haystack,” one of the investigators observes – clunk!).

As armed police swarm through the building and Wash handles the van bomb in a haze of turquoise smoke, we, the audience, are left to speculate on the identity of the sniper. Could it be policeman John, mysteriously absent from the scene and whose locker has been found to contain a copy of the London A-Z with some suspicious annotations? Or could it be Billy, fuelled by nationalistic fervour and who has tried on multiple occasions to join the army? Or might it even be our favourite lime-and-soda drinker, Karl, who was out in Afghanistan and presumably knows how to handle a rifle?

We won’t find out this episode, or, I suspect, the next. But for Lana and Sonia (Kerry Godliman) at the very least, their thinking has evolved beyond the simple Islamists or white supremacists binary. “They know how we think, how we move, everything,” Wash observes, “it’s got to be an inside man.” It seems like Trigger Point, which often feels likeLine of Dutybut with a few more bangs, is on the trail of a bent copper…