A Moth In Darkness. Changeling Race, #1

Liz Larson is fairy touched, a revel Dancer struggling with an addiction to fairy food and the lure of her own memories. When a strange elf turns up with an old photo and a new mission, Liz has only one answer for the uptight agent. No way. Never again. Marcus Bramble is not interested in babysitting a human junkie, but a series of ghastly murders has spread terror across the Fey lands. Only the fairies know what's going on, and only one person can get the little devils to talk.
Unfortunately, Liz has no interest in cooperating... until the investigation points to her old partner. Until Lockland Sheen is involved. Now the elvin agent and the human Dancer set out to save both their worlds. Unfortunately, the more they rely on Liz's tie to the fairies, the closer she inches toward the madness that lurks behind her fantasies.