A huge one that often gets overlooked in these lists is 'The Thirty-Nine Steps' by John Buchan. It's the absolute archetype of the 'man-on-the-run' thriller. An ordinary chap gets framed for murder and has to flee across the Scottish moors while unraveling a spy plot. The pacing is relentless, and it invented so many tropes we take for granted: the wrong man accused, the cross-country chase, the ordinary citizen rising to the occasion. It's not psychologically deep, but for pure, breathless narrative drive that defined an entire subgenre, it's a stone-cold classic. You can see its DNA in everything from Hitchcock films to Jason Bourne.
I'm a sucker for a good mole hunt. 'The Secret Servant' by Daniel Silva (part of the Gabriel Allon series) involves a kidnapping that spirals into a vast conspiracy touching on European immigration, radical imams, and Cold War grudges. Silva's research is always impressive, and he ties together real-world geopolitical tensions into a cohesive, if occasionally alarmist, narrative. The intricacy can feel a bit like he's checking boxes on a current-events bingo card, but the tradecraft and the global sweep keep the pages turning.