An old spy is back in the game in the fourth season of ‘Slow Horses’

In Season 4 of “Slow Horses” on Apple TV+, the misfits and losers of Britain’s MI5 domestic counterintelligence agency — collectively known as the slow horses, a sneering nickname that speaks to their perceived uselessness — find themselves working a case yet again.

This time it involves their fellow reject River Cartwright and his far more respected grandfather David Cartwright, the former head of MI5. Once sharp, the old man (Jonathan Pryce) has become disoriented lately. When a visitor arrives at his quiet rural home, he greets them with the business end of a shotgun. Blood is spilled and the cavalry is called. Was it all a big mistake? Or is something more sinister going on connected to his bygone days on the job? The slovenly Jackson Lamb, the exquisite Diana Taverner and the assorted slow horses must figure it out.

Lamb (Gary Oldman) arrives and, with typical unemotional disinterest, IDs the body. Chances are, he’s lying about whose corpse lies splayed in that bathtub. It’s a choice that has all the hallmarks of the simple but necessary subterfuge that is Lamb’s stock in trade.

Meanwhile, a car bomb has exploded in London and Taverner (Kristin Scott Thomas, formidable as ever) is tasked with finding out what happened and preventing any further incidents.

Somehow the car bomb and that death in David Cartwright’s home are connected, which necessitates a sojourn to France, where someone has tried to raise a small army of killers from birth. For what purpose? Unclear. But this ragtag paramilitary operation has fallen apart now that its members have grown into adults. What remains are just a few thugs, but their leader (Hugo Weaving) has an important connection to old man Cartwright and lingering resentments have a way of, well, lingering. Weaving is especially good as an entirely realistic villain, playing him with an American accent and an American sense of entitlement.

If the show’s third season was unusually obsessed with guns, the violence here erupts with more thought and narrative purpose, and it doesn’t overstay its welcome. As a series, “Slow Horses” doesn’t offer tightly plotted, clockwork spy stories. Think too deeply about any of the details and the whole thing threatens to fall apart. But on a scene-by-scene basis, the writing is a delicious combination of wry and tension-filled, and the cumulative effect is wonderfully entertaining. Spies have to deal with petty office politics like everyone else!