It will be called Prague Fatale.
Here's what Kerr told an interviewer with Kirkus Reviews recently: "I am afraid I cannot discuss the plot of this book except to say that it is no longer called The Man with the Iron Heart. It turned out that there was another book with that title. My book, half of which is set in Prague, is now called Prague Fatale. It’s set in October 1941. Think the Golem of Prague with Nazis."
The Quercus Web site gives the title as The Prague Fatale.
So in addition to learning more about Bernie's time spent during the war, we should be getting the backstory of his marriage to Kirsten. Should be fun!