They call it 'Pulse' - a radio signal which has puzzled the world for 40 years. But now Toshiko Sato has solved it.
She's uncovered a message which leads her to Russia, and into an uneasy alliance with the KVI - the Russian equivalent of Torchwood. Toshiko needs to get into Zone 10 - a frozen wasteland which officially doesn't exist.
An intergalactic war was once fought in Zone 10. And it turns out there's a survivor.