If you're into the Gabriel Allon series, especially the first four books, you might enjoy the intricate spycraft and historical depth of Daniel Silva's other works. 'The Kill Artist' and 'The English Assassin' set the tone for Allon's world, blending art, espionage, and moral dilemmas. For something with a similar vibe, try Charles Cumming's 'A Foreign Country' or Alan Furst's 'Night Soldiers' series—both nail that Cold War-era tension and layered protagonist.
Another angle is the 'John Rain' series by Barry Eisler. It’s got that same gritty, assassin-with-a-code energy, but trades art restoration for corporate wetwork in Tokyo. The pacing and moral ambiguity feel familiar, though Rain’s tech-heavy approach gives it a modern twist. And if you crave more art-world intrigue, 'The Art Forger' by B.A. Shapiro mixes crime and canvas in a way Allon fans would appreciate.