I finished The Thirty-nine Steps by John Buchan to fulfill the “espionage novel” prompt. Touted as the first spy novel, it does have some charm. It was only 78 pages, thankfully. I couldn’t really recommend this one unless this genre is just your thing.
This genre isn’t really my thing. But, Eye of the Needle and The Key to Rebecca by Ken Follet are two of the best reads I’ve ever enjoyed, and they both happen to be espionage novels. I suppose if Presumed Innocent was the only legal thriller you’d ever read, it would be tough to go back to reading Earl Stanley Gardner’s Perry Mason series.