The most dangerous secret in Amy and Dan's past is unveiled in Book 7 of the #1 New York Times bestselling series.

The hunt for 39 hidden Clues that lead to an unimaginable power has taken a heavy toll on fourteen-year-old Amy Cahill and her younger brother, Dan. They've just seen a woman die. They're wanted by the Indonesian police. They're trapped on an island with a man who knows too much about the death of their parents. And a tropical storm is rolling in.

Just when they think it can't get any worse, it does. Because the Cahills have one more rattling skeleton for Amy and Dan to discover... the terrible truth about their family branch.

Betrayed by their cousins, abandoned by their uncle, and with only the slimmest hint to guide them, fourteen-year-old Amy Cahill and her younger brother, Dan, rush off to Egypt on the hunt for 39 Clues that lead to a source of unimaginable power. But when they arrive, Amy and Dan get something completely unexpected - a message from their dead grandmother, Grace. Did Grace set out to help the two orphans... or are Amy and Dan heading for the most devastating betrayal of them all?