Second Grave on the Left (Charley Davidson #2) by Darynda Jones

If you hang around with dead people, life can get pretty complicated. Take it from Charley Davidson, part-time private investigator and full-time Grim Reaper. Complicated is her middle name. The deceased find her very sparkly. Demons find her irresistible. And one entity in particular wants to seduce her in every way possible.

When Charley and Cookie (her best friend/receptionist) have to track down a missing woman, the case is not quite as open and shut as they anticipate.

Cookie's friend Mimi disappeared five days earlier. Mimi then sends Cookie a cryptic message telling Cookie to meet her at an nearby coffee shop. The coffee is brewing, but Mimi's still missing. There is, however, a clue Mimi left on the bathroom wall: a woman's name. Mimi's husband explains to them that his wife had been acting strange since she found out an old high school friend had been murdered. The same woman whose name Mimi had scribbled on the bathroom wall.