The Rembrandt Affair by Daniel Silva

Determined to sever his ties with the Office, Gabriel Allon has retreated to the windswept cliffs of Cornwall with his beautiful Venetian-born wife, Chiara. But once again his seclusion is interrupted by a visitor from his tangled past: the endearingly eccentric London art dealer Julian Isherwood. As usual, Isherwood has a problem. And it is one only Gabriel can solve.
In the ancient English city of Glastonbury, an art restorer has been brutally murdered and a long-lost portrait by Rembrandt mysteriously stolen. Despite his reluctance, Gabriel is persuaded to use his unique skills to search for the painting and those responsible for the crime. But as he painstakingly follows a trail of clues leading from Amsterdam to Buenos Aires and, finally, to a villa on the graceful shores of Lake Geneva, Gabriel discovers there are deadly secrets connected to the painting.