Nemesis - Scott Ciencin

When an old friend from graduate school asks her for help with her job at a top scientific facility, Fred is torn between apprehension at renewing ties to her past and regret for the quiet life she might have led as a physicist entrenched in laboratory research. But on the night they are supposed to meet, her friend is gunned down in cold blood -- seemingly the innocent victim of a mob hit gone wrong.
Meanwhile Angel and Co. have been called upon to solve a series of grisly murders. Someone is taking out spellcasters who have, until now, been instrumental in preventing an apocalyptic breach of the barriers which separate our reality from that of other, more deadly dimensions.
Fred has a different mission, taking the place of her friend in order to find out the truth behind her death. But when the worlds of scientific research and supernatural killings begin to collide, it is up to her to piece the puzzle together and find the link that will help them save the world.