The Forgotten Ones: Book 1 (The Danaan Trilogy)

Allison O'Malley's plan is to go to grad school so she can get a good job and take care of her schizophrenic mother. She has carefully closed herself off from everything else, including a relationship with Ethan, who she's been in love with for as long as she can remember.

What is definitely not part of the plan is the return of her long-lost father, who claims he can bring Allison's mother back from the dark place her mind has gone. Allison doesn't trust her father, so why would she believe his fairy tale about a long forgotten Irish people, the Tuatha de Danaan? But truths have a way of revealing themselves. Secrets will eventually surface. And Allison must learn to set aside her plan and work with her father if there is even a small chance it could restore her mother's sanity.