Slow Horses is finally back on our screens and episode one is magnificent.

The fourth outing of the Gary Oldman-fronted spy thriller questions what happens when old age kicks in and an agent starts to lose their grip on reality, as well as the secrets they’ve been forced to keep over the years.

** Warning, spoilers for Slow Horses season 4 episode 1 ahead **

Bomb blast opens the show

The episode opens with a bang, quite literally, with a bomb blast ringing out across the capital as Roddy (Christopher Chung) sits in a chicken shop waiting for the rest of the Slough House gang to turn up at their Christmas party. 

Spoiler alert, there isn’t one. It’s Jackson Lamb’s (Gary Oldman) idea of a prank.

The explosion is no joke, though, with Westacres Shopping Centre going up in flames after IT consultant Robert Winters sets off a car bomb – but not before sending a chilling message in a pre-recorded video.

“You have crushed me. Only now will I be free. You will suffer for the years I spent imprisoned by your system. You will hear from my brothers soon,” he warns.

And we do… But there’s the small matter of River Cartwright’s death (Jack Lowden) to run through first.

‘You’re not my grandson’

We first catch up with River in a cafe telling Louisa (Rosalind Eleazar) that he’s been putting off visiting his grandfather, retired spy David Cartwright (Jonathan Pryce), as his apparent dementia worsens. 

After he tells her that David has struggled to remember him during his recent visits, Louisa urges River to go and see his grandfather – words she soon comes to regret.

Over at David Cartwright’s not-so-humble abode, he’s becoming increasingly confused. Outside, he’s convinced there’s someone in the grounds. “Come on, let me see you, I know you’re there,” he says, before dashing inside the house with his shotgun and falling asleep.

He’s woken by a man at the door. “Can you let me in, I’m getting soaked,” we hear River’s voice say. Crucially, however, we don’t see River’s face.

“I’m just going to run to the loo,” River says, heading upstairs. “Shall I run you a bath while I’m up there?”

Looking at a picture of himself with River, David decides that the man in the house isn’t his grandson and reaches for his shotgun.

Heading upstairs, he tells the man: “You’re not my grandson,” and shoots him twice. Somewhat predictably, one lands square in the face.

Cue Jackson Lamb arriving on the scene to ID the body.

“Does he have any identifying marks?” he’s asked by Emma Flyye (Ruth Bradley), Duffy’s replacement, as the head of MI5’s internal security division, the Dogs.

“Well he used to have a face,’ Lamb drawls, before confirming it’s him.

Mystery solved…?

Over at Slough House, news spreads of River’s death as Roddy pinches his computer because he doesn’t need it any more and Louisa blames herself.

Lamb then heads over to tell Catherine Standish (Saskia Reeves) River’s been killed and David’s missing.

No longer a Slow Horse, she doesn’t ask for any details… and Jackson soon works out that’s because she knows that River is actually alive.

In a bit of a clue even the most amateur sleuth could crack, River’s car is parked outside Standish’s flat, and she’s soon forced to admit that he was there but isn’t now.

David is, though.

“Please don’t pretend you haven’t got the old bastard stashed in the bedroom,” says Lamb, as he walks in to find a sleeping David Cartwright.

“Happy now?” Standish asks. “You know me, when am I not full of joy de fucking vivre,” Lamb tells her.

Waking David up, he demands to know where River is, before action cuts to River in a cab in the French countryside.

Clearly not there on holiday, he’s on the trail of the man David did actually shoot in his bathroom, having found his French passport.

“Who the hell are you?” he says to himself while looking at the passport in the back of a cab.

Speaking in French, he asks the driver: “How much longer?” “We aren’t far now,” he’s told, as French rap music takes us to the closing credits.

So who is the man Cartwright Snr killed?

According to the book it’s based on, Mick Heron’s Spook Street, he’s a man connected to an old mission from David’s Cold War past while he headed up MI5.

But will the series follow the novel? Does David really have dementia? What does Standish know? Will Flyye figure out that River isn’t actually dead? Who is the car bomber connected to, and will his brothers strike again? And will Jackson Lamb ever do what everyone who’s ever met him wants and have a good old scrub?

Roll on next week when we (probably won’t) find out.

New episodes of Slow Horses drop on Apple TV+ every Wednesday.