Bestselling author Katherine Reay returns with an unforgettable tale of the Cold War and a CIA code breaker who risks everything to free her father from an East German prison.

From the time she was a young girl, Luisa Voekler has loved solving puzzles and cracking codes. Brilliant and logical, she's expected to quickly climb the career ladder at the CIA. But while her coworkers have moved on to thrilling Cold War assignments—especially in the exhilarating era of the late 1980s—Luisa's work remains stuck in the past decoding messages from World War II.

Journalist Haris Voekler grew up a proud East Berliner. But as his eyes open to the realities of postwar East Germany, he realizes that the Soviet promises of a better future are not coming to fruition. After the Berlin Wall goes up, Haris finds himself separated from his young daughter and all alone after his wife dies. There's only one way to reach his family—by sending coded letters to his father-in-law who lives on the other side of the Iron Curtain.

When Luisa Voekler discovers a secret cache of letters written by the father she has long presumed dead, she learns the truth about her grandfather's work, her father's identity, and why she has never progressed in her career. With little more than a rudimentary plan and hope, she journeys to Berlin and risks everything to free her father and get him out of East Berlin alive.

As Luisa and Haris take turns telling their stories, events speed toward one of the twentieth century's most dramatic moments—the fall of the Berlin Wall and that night's promise of freedom, truth, and reconciliation for those who lived, for twenty-eight years, behind the bleak shadow of the Iron Curtain's most iconic symbol.