A dark lord from another universe. A lonely young woman. A fateful meeting between them changes both their lives forever—and leaves the fate of two worlds hanging by his forgotten past.

In another world, a dark mage called the Storm Lord fights for his life. As his enemies breach the walls of his fortress, he opens a portal between realities. He leaps, tumbling into darkness.

Driving along a gravel road in California's Sierra foothills, Ro Cheney wishes she had someone, anyone she could count on. 

A black hole opens and spills a man onto the road. He's wounded, strangely dressed, doesn't speak English—and doesn't even remember his own name. When she lays a compassionate hand on his shoulder, the shoulder of a man who has known nothing but violence and hatred, she sets an bond between them.

Ro names the man Blackthorne, never realizing how dangerous he is. But a rare friendship grows between them, and they begin to change one another in ways that neither understands.

But the past won't rest. Hunting the Storm Lord across the worlds are five vengeful mages, determined to destroy the monster who devastated their own world. Before he faces them, he must battle a far more terrible enemy within—the Storm Lord himself, who struggles to emerge from the darkness of Blackthorne's buried memories.