He is a man who notices things, the dad in the train carriage – even while he is watching his two children sleep. A man acting oddly before he gets on. A toilet door closed for too long. A guard lingering a beat on a passenger of a certain ethnicity. In quick succession he has confirmed there is an alert out for a potential suicide bomber on the train and that his best course of action is to fling them off as soon as he comes out of the loo.

He may be a knackered parent of two, but he is also the special protection officer David Budd (Richard Madden) and throwing people off trains instead of letting them detonate bombs is what he does. The person under suspicion leaves the toilet without any signs of a vest, but when David examines the loo he finds the real bomber – the terrified young wife of the suspect, strapped into a suicide vest. Budd calmly introduces himself in Arabic, negotiates and then wraps his arms around her so the snipers at the depot cannot shoot her. Everyone is saved! He is rewarded with a promotion. From now on, he will specially protect the home secretary, Julia Montague (Keeley Hawes)! Hurrah!

The first 20 minutes of Bodyguard would be pure James Bond if it were not for the fear and doubt that convulse Budd when he is preparing to do his flinging or his saving. For this is a Jed Mercurio drama, and any standard tropes are there only to lull you into a false sense of security while his characters start dismantling everything around them.

Mercurio specialises in subverting not just narrative expectations, but also collective complacencies. He put his own bomb under the nation’s view of the NHS as a semi-divine institution run by saints in his first show, Cardiac Arrest, and then again in the equally magnificent Bodies. And what he has done to any vestigial faith in the police service through four series of Line of Duty does not bear thinking about. The fifth series following the investigations of the anti-corruption unit AC-12 starts shooting next month and, if the rumours I have been hearing are anything to go by, it promises to undo us all.

In Bodyguard, Mercurio trains his eye and his nose for corruption on the corridors of power and, by the end of last night’s opening episode, it was clear he has created something as dark and moreish as ever. As the credits rolled, I snouted for more like a truffle-hunting pig.

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Budd is not Bond. He is a former soldier back from Afghanistan, with PTSD barely under control and nursing a burning resentment towards the people who sent him there, further stoked by a meeting with an old mate from Helmand. A robotic professional on duty (there is a lovely scene in which he lends a coffee-stained Montague his shirt before a TV interview: “It’s altered to fit over my ballistics vest, so the chest to waist ratio should be compatible”) with circuits sparking dangerously beneath, he broods in the dark over a recording of the interview in which Montague refuses to apologise for supporting military action overseas.

It’s a fine performance from Madden – who came to prominence as Robb Stark in the first three seasons of Game of Thrones, a show in which all actors took second billing to the set dressing – and just as fine a one from Hawes. Her glacial poise and intelligence mesh perfectly with a home secretary who is variously described as “a sociopath” (her PA), overambitious (her ex-husband, whom I am paraphrasing for a family newspaper) and a former criminal barrister who simply wants to be in a better position to help people (Montague herself).

She is pushing, in the wake of the train incident, for heightened surveillance and security powers for the state. Or using it to further her own agenda. Or exploiting fears to position herself for a leadership bid. In Mercurio’s world, as in life, there is no such thing as pure motivation for anyone, least of all politicians.

So, here we are, ready to have our world viewed, our issues anatomised and our psyches probed by the story of a relationship between an unstable stoic and a potential sociopath, fashioned by a master. Truffles, truffles, truffles, my friends, all the way down.