Chain Letter by Claire McNab

TO WHOM IT MAY CONCERN: You are a chosen one. Your name has been selected to receive these instructions. Follow them exactly and you will have great good fortune. Fail, and this letter will bring you death. You have forty-eight hours.
Do not break the chain... While investigating the murder of a fellow police officer, Australian Detective Carol Ashton believes she has discovered a bizarre link between this case and several other unsolved homicides - each victim received a chain letter promising death if the instructions are not followed. When her hunch leads nowhere, Carol figures it was just a coincidence. Then, someone very close to her receives a letter.