Insidious

True evil is rarely obvious. It is quiet, patient. 
Insidious. 
Awaiting the perfect moment to strike. 
Joy Malone finally knows who she is, where she comes from and how to live in two worlds at once. And now she can introduce her family and friends to her mysterious boyfriend, Indelible Ink. But when Ink's twin sister, Invisible Inq, calls in a favor, Joy must accept a dangerous mission to find a forgotten door between worlds—a door hiding a secret that some will kill to keep. 
Unseen enemies, treasonous magic and an unthinkable betrayal threaten both the Twixt and human worlds as Joy races to expose an ancient conspiracy and unleash the unalterable truth—some secrets cannot remain secret forever.