After returning from an all-out war in Mexico, Jax Aubrey, his guardian, Riley, and liege lady, Evangeline Emrys, are in hiding. So when a man named Finn Ambrose tracks them down, claiming to be Jax's uncle, their defenses go up.

As it turns out, Uncle Finn is part of the Dulacs, a dangerous enemy clan. After the Dulacs kidnap Jax's best friend, Billy, in order to lure Jax to their residence in Manhattan, Jax has no choice but to go to the city on his own or risk endangering Riley and Evangeline.

There, he meets Uncle Finn; his cousin, Dorian; and the rest of his crooked relatives—plus he inadvertently stumbles upon a maze of magic tunnels beneath their apartment building. And what Jax finds there could put the entire Eighth Day and the Emrys bloodline in jeopardy.