All over the world, random people are being brutally assassinated.

Each death is unique, but they all have one thing in common: four numbers branded or carved into the victims' flesh.

What does it mean?

For the brilliant and haunted CIA analyst Quinn Mitchell, it means leaving a safe and predictable desk job as she tries to track down a global serial killer.

What she doesn't know is that nothing about this mission - her handlers, the intelligence, even the laws of cause and effect - can be trusted.

And her target has saved his most shocking murder for last . . .