Rachel Innes, a middle-aged woman decides to spend a summer in a summer house with her niece and nephew. She found what seems to be a perfect place for this, only this perfect place appeared to be haunted the first night Rachel spends in there. In addition to this, a dead body appears in the house some time later. If you think this is bad, mysterious events further down the road make haunting and dead body pale in comparison.
I really like the character of Rachel Innes. She appears to be an intelligent strong woman (especially considering the time when the book was written). On the other hand, her maid Libby is a coward basically providing a comic relief to the plot. Speaking of annoying characters Rachel's niece and nephew mentioned above definitely deserve to be spanked for their behavior regardless of their age.
All in all, the book has enough plot twists and mysteries to keep its reader completely absorbed and lost in the plot. I also need to mention this book in available at Project Gutenberg, and is one of the best mystery novels in there.