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 theyve 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 isnt one. Its Jackson Lambs (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 theres the small matter of River Cartwrights death (Jack Lowden) to run through first.

Youre not my grandson

We first catch up with River in a cafe telling Louisa (Rosalind Eleazar) that hes 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 Cartwrights not-so-humble abode, hes becoming increasingly confused. Outside, hes convinced theres someone in the grounds. Come on, let me see you, I know youre there, he says, before dashing inside the house with his shotgun and falling asleep.

Hes woken by a man at the door. Can you let me in, Im getting soaked, we hear Rivers voice say. Crucially, however, we dont see Rivers face.

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

Looking at a picture of himself with River, David decides that the man in the house isnt his grandson and reaches for his shotgun.

Heading upstairs, he tells the man: Youre 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? hes asked by Emma Flyye (Ruth Bradley), Duffys replacement, as the head of MI5s internal security division, the Dogs.

Well he used to have a face, Lamb drawls, before confirming its him.

Mystery solved?

Over at Slough House, news spreads of Rivers death as Roddy pinches his computer because he doesnt need it any more and Louisa blames herself.

Lamb then heads over to tell Catherine Standish (Saskia Reeves) Rivers been killed and Davids missing.

No longer a Slow Horse, she doesnt ask for any details and Jackson soon works out thats because she knows that River is actually alive.

In a bit of a clue even the most amateur sleuth could crack, Rivers car is parked outside Standishs flat, and shes soon forced to admit that he was there but isnt now.

David is, though.

Please dont pretend you havent 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, hes 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 arent far now, hes told, as French rap music takes us to the closing credits.

So who is the man Cartwright Snr killed?

According to the book its based on, Mick Herons Spook Street, hes a man connected to an old mission from Davids 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 isnt actually dead? Who is the car bomber connected to, and will his brothers strike again? And will Jackson Lamb ever do what everyone whos ever met him wants and have a good old scrub?

Roll on next week when we (probably wont) find out.

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