We should be so lucky. That the best spy thriller series in recent years, the Jackson Lamb adventures by Mick Herron, could end up being converted into a spellbinding TV series, goes against all my experience of screen adaptations. Season 1 was a kinetic introduction, Season 2 struck me as perfect, and Season 3 continued the high standard. The fourth season of Slow Horses amends the storyline of one of the best Herron books but retains the heart of that author’s plotting triumph. Gary Oldman continues to live and breathe the obnoxious but formidable spy maestro Lamb, managing to convey (as do Herron’s books) the oafishness and brilliance without drifting into caricature. In this episode, though, Jack Lowden nearly upstages him as the earnest, superhero-wannabe River Cartwright. When River’s old father (formerly a spy eminence) sinks toward dementia and a villain comes calling, River is plunged into an adventure that incorporates a mystifying trip to France, a terrorist bombing back in England, a relentless assassin, and an evil mastermind (played wonderfully by Hugo Weaving). Wonderful plot twists, the continued excellence of the supporting cast of “slow horses,” spot-on music, and gritty cinematography … Season 4 is yet another gold standard for modern series TV.

