The Rembrandt Affair by Daniel Silva

Determined to sereve his ties with the Office, Gabriel Allon retreated to the windswept cliffs of Cornwall with his beautiful wife, Chiara. But once again, his seclusion is interrupted by a visitor. The visitor is a art dealer by the name of Julian Isherwood. Isherwood would like Gabriel to find a painting by Rembrandt that was stolen from the person that was restoring for Isherwood. Gabriel says "yes" to this request. What start as a simple quest to find a missing painting turns into quest to keep Iran from starting a nuclear program. It is rather long, but you won't want to stop reading. Very entertaining. I couldn't put it down. PatM