Is it a poltergeist or a very capable human doing all the mischief? Alexander Hero, psychic investigator goes to Lord Paradine's castle to figure it all out. Other wordly visitors, very human errors, a deep look at human personality, and an almost romance add up to an interesting tale.
This is an easy-to-read book, not at all in the "horror" genre, despite the ghostly goings-on. The blurb on one of the editions notes it as a "lovely ghost story or a ghostly love story." It's a light version of either, in any case.