The Maras Affair by Eric Ambler

Charles Burton, journalist, cannot get work past Iron Curtain censors and knows he should leave the country. However, he is in love with his secretary, Anna Maras, and she is in danger. Then the President is assassinated and one of Burton's office workers is found dead. He decides to smuggle Anna out of the country, but her reluctance impedes him, as does being sought by secret police and counter-revolutionaries alike.