Gary Gibson

Survival Game by Gary Gibson is the second book in the gripping apocalyptic duology that began with Extinction Game. Katya is a scientist, working on a classified project for the Russian Empire. She's also desperate. Her bosses want to exploit her knowledge and send her on an incredible, dangerous mission. And if she refuses, her father's life will be forfeit. Katya must retrieve an artefact that will grant new life to the dying Russian tsar.
She's therefore being sent deep undercover on an alternate version of Earth, to an American-controlled island. Here Borodin, the tsar's spymaster, will be watching her. On the island Katya and Jerry, an American adventurer, form an uneasy alliance. They discover the artefact will call down terror from the depths of space, yet Katya's superiors refuse to listen. But Katya and Jerry's worlds face extinction, so the artefact must be destroyed - at any cost.
Two civilizations depend upon it.