Prussian Blue von Philip Kerr

The French Riviera, 1956: The invitation to dinner was not unexpected, though neither was it welcome. Ernst Mielke, deputy head of the East German Stasi, has turned up in Nice, and he’s not on holiday. An old and dangerous adversary, Mielke is calling in a debt. He intends that Bernie go to London and, with the vial of Thallium he now pushes across the table, poison a female agent they both have had dealings with. 
But chance intervenes in the form of Friedrich Korsch, an old Kripo comrade now working for Stasi and probably there to make sure Bernie gets the job done. Bernie bolts for the German border. Traveling by night, holed up…