The Haunting of Hoover Dam (The Mystery House Series)

When Boulder City is inundated with strange occurrences, the local, state, and federal authorities come up emptyhanded. Motivated by heart-wrenching appeals on Sue's blog, Ellen and her friends offer to help. But the pressure's on like never before when their paranormal investigation is met with scrutiny at every turn, especially when they discover, with the help of a one-hundred-year-old ghost, a sickening coverup from the days of the building of the Hoover Dam.