The Lisbon Exchange. Marcus Vane Series, #1

For readers of John le Carré, Alan Furst, Mick Herron, and Charles Cumming. A dead mentor. A mole no one will name. A betrayal that has been waiting patiently for years. Fourteen months ago, intelligence officer Marcus Vane walked away - from the Service, from the work, from a mission that ended in disaster - and vanished into a quiet Greek harbour town where no one asks questions. Then his old mentor dies in a "routine" crash in the Austrian Alps, and Marcus knows an accident when he sees one.
This isn't one. What follows isn't a chase but an excavation. From Athens to Rome, Vienna to Lisbon, Marcus reads the silences, the paper trails, and the people - pulling one patient thread until a decades-old betrayal inside British intelligence begins to surface, and the quiet, protected figure at its centre realises he has finally been found. The Lisbon Exchange is a slow-burn, morally complex espionage novel in the tradition of the great spy writers: atmospheric, cerebral, and built on character and consequence rather than gunfire.
Book One of the Marcus Vane series. If you like your spy fiction quiet, European, and quietly devastating - start here.