Embrace the Wolf — Benjamin M. Schutz

The lovely little twin girls have been missing for five years, and the cops have long since dropped the case. But their father, Herb Saunders, is obsessed with finding the wolf who stole his lambs. A phone call taunts Herb with his daughters' voices, twisting the knife in a never-healed wound - and now Herb himself is missing. Leo Haggerty, Washington, D.C.'s best private eye, risks his license and his life on this case - to trap this deadly wolf in his lair.