Ben is stuck. His parents' divorce left him trapped in a backwater town, and he's just been caught breaking into a fairly big corporation's servers and they're going to try him as an adult.
Essa is also stuck. A vengeful ex-lover left her trapped in a backwater world, and she has no way back home to the Well, the vast bottomless pit lined with doors to countless realities.
A lucky accident (not so lucky for Ben) frees Essa and now they're both in the Well, with its invisible lizards, cities hung from cats'-cradles and Library made of sand.
Essa wants revenge. Ben wants a way home. The awakening of an ancient threat to the Well puts both their plans on hold. On the run, their only allies a clockwork spider and a girl made of iron, they'll have to work together to save all the worlds.