Banished by their MI5 betters to the mildewing outpost of Slough House in London, the disgraced British intelligence agents of “Slow Horses” — a nickname that reflects their “put out to pasture” limbo — are back for a second season on Apple TV+.

With its dark sense of humor and propulsive pacing, the linchpin of the series is the head outcast himself, Jackson Lamb. The new season doesn’t bother with a preamble but dives headfirst into the story: An aging British spy from the Cold War era is found dead on a bus. Heart attack, says the official report. Lamb suspects murder.

Rumpled, smelly and greasy-haired as ever, Gary Oldman’s performance elevates Lamb’s rancid presentation to high art. He’s a man of contradiction: Dissolute but shrewd. Convinced that something’s afoot, he decides to do some digging of his own into that death on the bus, and ropes in a few of his underlings for the job. Lamb has a hunch there is a Russian sleeper agent or two in their midst who may be responsible.

Separately, there’s a Russian oligarch living in exile in London with political aspirations back home. He has an eye on the top job apparently, and he’d like to set up an ultra-private meeting to discuss how the British government can help with that. So a couple of Lamb’s agents are tasked with setting up the security logistics for this clandestine affair. It’s shaping up to be a tense assignment, judging by the thuggish Russian bodyguards with whom they’re working.

Yes, these two seemingly unrelated storylines will intersect. Yes, you may need to watch the season twice to get a handle on how all the pieces fit together. (The series is based on the novels of Mick Herron; Season 2 is adapted from “Dead Lions.”) The plot snakes along, full of double-crosses and blind alleys, quizzical looks and long stares at security footage. I especially liked the banal details of a covert meeting that takes place at a laundromat. It’s a story built on greed, revenge and an elaborate assassination plot. But it also asks: Whose deaths matter to these spymasters — and when is it more expedient to simply look away?

River Cartwright (Jack Lowden) is in the mix as well. He’s the former golden boy who seems unlikely to live down the massive screw-up that landed him at the team’s sad excuse for an office where he remains stuck, despite his best efforts or his useless nepotism connections. His grandfather, wonderfully underplayed here by Jonathan Pryce, is the former head of MI5 now puttering around in his garden, doling out wisdom here and there, stingily, as if dispensed from an eyedropper.

But Lamb needs someone undercover in the Cotswolds to root out one of those Russian sleeper agents, so he taps River for the job and you can practically see the young guy’s thoughts form in a bubble over his head: Finally, some action! Lowden has a great presence, eager and alert. But he’s off on his own for most of the season, which isn’t as much fun as seeing him mix it up with his colleagues, especially Lamb.

Also: Instead of mucking around in any of the class issues that define the Cotswolds region, so beloved by the rich with their pricey country homes, the show portrays the area as simply any old English village. Even so, there’s a halfway decent running joke that sees River backed into situations where he’s handing over cash, time and again, just to do his job — how can he afford it on his surely less-than-lucrative Slough House salary? The countryside isn’t a bad setting; it offers a wonderfully lush and green visual counterpart to the glass, metal and concrete of the city, or the dingy browns and yellows of Slough House.

Rosalind Eleazar (as Louisa Guy, the practical-minded half of that security team assigned to the aforementioned meeting) and Saskia Reeves (as Catherine Standish, who functions as an office manager for Lamb and is wilier than anyone gives her credit for) both see their roles elevated this season in some genuinely compelling ways. They’re not dashing types like River, but more low-key in their approach — until they each meet a situation that requires they turn up the heat.

Part espionage story, part workplace comedy, the plotting this season lacks a certain elegance. Is Lamb really much of an intelligence man if he’s notorious among washed-up Russian spies and British private security contractors alike? Maybe that’s one of the reasons he’s been shoved off to Slough House, but no one ever comments on what appears to be a very inconvenient reality: Everyone knows he’s a spy.

Kristin Scott Thomas is back as the elegant-icy Diana Taverner, MI5’s No. 2 — or in the show’s jargon, head of the Second Desk. But she’s reduced to a reactive presence this time out, which sells the character short. She’s much too callous and self-interested to be yanked around like an exhausted bureaucrat, pinballing from one annoyingly self-important man to the next.

These are minor complaints. The show (which has been renewed for two more seasons) has real energy. It’s funny and feels smart even when it’s not, with a focus on small and specific stories over the outsized global bombast that tends to dominate espionage stories at the moment.