Some secrets are worth killing for. Others are worth killing everyone to keep.

When a retired CIA courier is found murdered in a luxury Vienna hotel, investigators focus on the cause of his death.

Otis Thorne notices something else.

The envelope the killer left behind.

Inside is a list of retired intelligence couriers dying across Europe from what appear to be natural causes. Heart attacks. Accidents. Suicides. But someone is systematically erasing the last people who remember the hidden routes of a Cold War courier network.

With hacker Noah Pye racing to identify the next target, Otis follows a trail from Vienna to Kraków and Prague, uncovering a covert operation buried for decades inside the intelligence community itself.

The couriers were never supposed to know the secrets they carried.

Now someone is making sure they never tell them.