Footsteps in the Dark was first published in 1932. I love mysteries from that era. While this book isn't the finest mystery ever written, it was still a lot of fun.
Charles and Celia Malcolm, Celia's sister Margaret and brother Peter, and their aunt Mrs. Bosanquet have all inherited an ancient property known as the Priory. It's a picturesque place despite its lack of modern conveniences--like electricity--and they decide to stay there for the summer. But the Priory is locally infamous for being haunted by the sinister figure of a monk. Before long, the family hear footsteps and unearthly groans. Charles and Peter are determined to discover who's behind what they're sure is the only rational explanation: that one of the strangers lurking in the area is trying to drive the family away from the Priory for some purpose.
The book is surprisingly long, much longer than it really needs to be. The pace is slow. Characters recount to each other events that the reader has already witnessed, or repeat conversations the reader has already heard. But it's also a fun mystery, with lots of eccentric characters--from an entomologist supposedly searching for rare moths on the property at night, to a drug-addled French artist who fears and loathes the ghostly monk. There are skeletons and secret passages, people who aren't what they seem, suspicious-sounding conversations overheard.
While the plot is kind of absurd, there's a charming 1930s feel in the murderer's elaborate scheme. The subplot of a romance between Margaret and another character is abrupt but sweet. I can't say this is the best mystery I've ever read--it just moves too slowly and I did actually guess the murderer well ahead of time--but it was certainly entertaining and worth keeping.