Charlie said these two had been one big book, which is probably why a lot of unanswered plot lines in the first were answered in the second. Miriam starts setting up business in the third world, runs into a Leveller who helps her, and buys herself a mansion. She's attacked by the lost thread of the Clan -- the original son was sent West and lost everything he had and had to remake the knotwork and got it wrong so his descendants walk between world one (the medieval world) and world three. They don't know about our world (world two). Also, her uncle has called an extraordinary meeting of the Clan, on her request, and that brings forth more that's been hidden. At the same time, a trusted non-walker employee decides to tell the DEA and CIA about the Clan, booby-traps the world one stronghold, and escapes. The Clan manages to get together and tries to save non-walkers who are in our world from the feds.
This was a breathless book -- things are always happening and happening wrong. There's betrayal, assassination, discovery, and prejudice. I enjoyed it greatly and am sorry it will be a couple weeks before I can start the next: Clan Corporate.
You can't read this first, but why would you want to when the first book is also excellent? Highly recommended.