Cassie Robinette, a young American traveling overland around the world, arrives in Kabul in August 1978 and meets two other travelers. Twelve days later, they cross the Afghan border together into Iran. Meanwhile, her friend Jack Hunter waits for a letter about meeting her in Istanbul. None comes. In time, he sadly assumes she has moved on without him. But 29 years later, when he tries to locate her again, he can find no trace. Sometime in September 1978, she vanished. Determined now to find her, he mines her old letters for clues and tracks down people she left behind. As he pieces together the puzzle of her disappearance, he begins to grasp the terrible danger that threatened her. And discovers that someone else from her past, someone deadly, is also on her trail.