Ghost of a Chance (Welcome Inn #2) by E. L. Flood

Molly O'Brien can't wait to explore the maze of tunnels she discovers beneath Welcome Inn. But she never expects the hidden passages to lead her to a ghost!

Molly is sure she's discovered the spirit of Mary McPhail, whose father was unjustly hung for murder a hundred years ago. Molly and her sister. Gwen, are determined to solve the riddle of Mary's death. But a series of strange and dangerous events lead the girls to wonder: Does Mary McPhail want the mystery solved? And how far will she go to stop them?