Supernatural the book of monsters, demons, spirits and ghouls

Death Apparitions, part 1

Not all spirits are out for revenge. Sometimes they just want justice. Take the case of a woman named Claire Becker, murdered by her lover, who was a crooked cop in Baltimore. We had to do a little more interacting with the local PD than is usually our preference, mostly because they though we were serial killers.
Until one of the Baltimore cops, Diana Ballard, saw the ghost of Claire Becker. That bought us enough slack so that we could do some investigating and discover that Claire's murdered was Ballard's partner.
Awkward.
The way it all came together was that we figured out that Claire wasn't a vengeful spirit-she'd had plenty of chances to off all of us by then. She was a death omen, a spirit that appears to people to warn them of their doom-which in this case meant warn everyone involved that Ballard's partner, Peter Sheridan, was gunning for them.
Some death omens are quiet. They don't all howl like your proverbial banshee. An apparition of an individual can signal that person's death. The Germanic doppelgänger, the Scandinavian vardogr, the Icelandic fylgia, the Finnish etiainen, they're all manifestations of bilocation: the phenomenon of appearing in two places at once. Sometimes bilocation is the result of distress; the etiainen generally appears when a shaman or someone in extreme circumstances is reaching out to the person with whom they share the closest emotional relationship. It's not a big step from there to a death omen. Most apparitions of doubles foreshadow death in one way or another. Sometimes the apparition appears suffering the wounds that the person will die of, but more often the plain fact of the apparition is enough to signal that death is near.
Sometimes a death apparition appears to warn other people, like in Claire Becker's case. We got the message just in time, as it turned out, and Diana settled things with Officer Sheridan before she could meet an untimely death.