"...a master of core sf" - The Guardian. Rozalia is a Pathfinder, dedicated to exploring parallel Earths where mankind has been wiped out. As a survivor of one such world, she's seen every kind of apocalypse possible. All she and her fellow Pathfinders want is a new home-both for themselves and for the organization that brought them together. Now, at last, they've found one: an untrammeled Eden where humanity never even evolved. But just when it looks like their work is finally over, the Pathfinders find themselves confronted by new threats. Someone has been accessing an off-limits alternate in search of weapons that could destroy them all; samples of their most advanced-and dangerous-technology have been stolen from a research facility, and toxic rain is driving people crazy-which means she might be going crazy too. Either that, or they really are being invaded from another dimension. The Pathfinders have no choice but to come together one last time and journey across Earths left lifeless by rogue singularities or littered with ancient and perilous ruins. If they don't, an entire world dies...and millions with it.