Books in the The Devil's Gospel series

Biology Professor Kevin Ballard finds his quiet life rocked by a series of vicious mysterious events. First, his mother is slain in his childhood home. Then his girlfriend (and research assistant) is kidnapped from their cabin and he finds that the plant he's studying is apparently being used in strange local rituals. To top it all off, the police think Kevin is somehow involved. Who wants to wreck his life and why?