A dead colleague. A package of encrypted letters. And a secret that was supposed to stay buried since the Cold War.

Former NSA signals intelligence analyst Elena Voss traded classified intercepts for quiet lecture halls at Georgetown - until a mysterious parcel drags her back into the shadows. Inside: photocopied letters from WINTERGARDEN, a Cold War dead drop network that was officially shut down decades ago.

Except it wasn't.

As Elena cracks layer after layer of encryption, she uncovers a chilling truth: a network of sleeper agents, planted before the Berlin Wall fell, has reactivated. Their target? A weaponized chimeric virus hidden beneath a prestigious Prague research institute - a doomsday insurance policy engineered in a secret Soviet lab and never recovered.

Now, with a mole inside the NSA tracking her every move and a ruthless handler known as "The Librarian" eliminating loose ends, Elena and an aging former MI6 operative have six days to stop an underground arms auction in Vienna that could unleash a nightmare on the world.

The clock is already running. Start reading now.