A little late in the day, real life having intervened, here is a wrap-up of Bodyguard (BBC1).

Jed Mercurio’s six-part thriller was an impressive runaway train of a drama – a fitting analogy, as the opening scenes on a train constituted the most thrilling television seen in ages.

An average of 10.4 million viewers watched this thriller, according to the BBC, so Mercurio must be doing something right. No one can deny that he delivers a story at unstoppable pace. The Line of Duty writer knows more about narrative propulsion than a party of thriller writers trapped in a falling lift.

His greatest achievement was to get so many people watching a TV drama in the old-fashioned way – as it went out, once a week in a retro-rush, instead of doing a binge. This was talked-about water-cooler television, even if you get your water from the cold tap in the kitchen.

The last drama to attract that many viewers was the finale of season two of Downton Abbey – a denouement that did without this Downton refusenik.

In case you’ve had you head in the fridge for six weeks, Bodyguard is a thriller starring Richard Madden as ex-soldier turned protection office David Budd. Or starring Richard Madden as his frown, for he does an awful lot of that.

Anyway, about last night.

The 75-minute finale was, strangely, the weakest episode yet. This was down to various faults, but mostly it was down to that extra 15 minutes. While the other episodes were tight and racy last night’s conclusion was oddly flabby, until rescued with a final rush of breathless brilliance.

The writing wobbled at times, especially when DS Louise Rayburn (Nina Toussaint-White) turned on Madden, having preciously been Budd’s buddy. Louise started shouting at Budd, a little unkind as he had a bomb strapped to him at the time. That bomb didn’t go off, but her acting did.

The denouement when it came was fine, even if the action had swerved between high drama and farce, like two cars colliding. And farce left some of its paint on drama’s front wing.

Like many thrillers that start out so well, Bodyguard didn’t quite live up to its opening promise, and threatened to underwhelm. It didn’t do that in the end, but it was a close-run thing.

Fortunately, Mercurio’s skill at wrongfooting his viewers survived until the end. Various theories that rattled the internet turned out to be wrong. Home Secretary Julia Montague really was dead – unless she wasn’t, as some conspiracy theorists think they spotted her at a window in one scene.

What about Budd’s wife’s new boyfriend? Mentioned often but never seen, he was trailed as a potential key to everything. Nope. And that dodgy baldie in glasses (and you should always keep your eye on those) who took Montague’s job – what was he up to?

And what about Commander Anne Sampson (Gina McKee): was she a flapping loose end, or had she been wearing a red herring suit all along?

Best twist of all led right back to the beginning. Suicide bomber Nadia wasn’t a mistreated wife under her husband’s cruel thumb, but a fully committed evil-genius bomb-maker and terrorist. Didn’t spot that one before it rolled through the interview room door.

Did those of us who loved Bodyguard get a touch carried away and were we a little short-changed by the last episode? Yes, but it was still a thrilling ride.