Poltergeist. Number 2 in series

Meet Harper Blaine. She doesn't just see dead people... Harper Blaine was your average small-time PI until she died - for two minutes. Now she's a Greywalker - walking the thin line between the living world and the paranormal realm. And she's discovering that her new abilities are landing her all sorts of "strange" cases. In the days leading up to Halloween, Harper's been hired by a university research group that is attempting to create an artificial poltergeist.
The head researcher suspects someone is deliberately faking the phenomena, but Harper's investigation reveals something else entirely - they've succeeded. And when one of the group's members is killed in a brutal and inexplicable fashion, Harper must determine whether the killer is the ghost itself, or someone all too human.