The Mystery of the Empty Room.

Ruth and her father stay at an inn run by the malicious Scroogles. The Scroogles rob Ruth's father, throw his seemingly dead body over a cliff, and deny he was ever there when Ruth asks. Ruth seeks help from artist Richard Foster. Together, they find evidence, confront the Scroogles, leading to a struggle where Mr. Scroogles accidentally kills his wife before being shot and dying himself. Ruth and Foster (now engaged) find her father alive but dazed; he recovers, and adopts a mistreated girl from the inn. The traumatic "empty room" incident leaves a lasting impression on Ruth.