It isn't until one night after her father--the houses machinist--goes to sleep behind the boiler down in the basement (no one knows he lives down there after his duties are done), she sees a mysterious cloaked figure chasing down one of the children of a visitor of the manor. The child becomes enveloped by this cloaked man and disappears. She later finds out that more children have gone missing without a trace. Serafina has to help find them even though no one believes her beside her one new friend and his trusted dog.
Overall, it is a fair book, written well, with believable characters. There are some instances of cheesy-ness, but I think that may have to do with its originally intended audience (approximately ten year olds). Things get wrapped up neatly and everything is made out fine. Even when her cover is blown and the adults of the house find out she has been living in the house for her whole life, the don't seem to mind... That is a bit bothersome.
I will say though that unlike many of the other junior fiction I've read, this has a lot more adult conversation and presence than most. Though many of the adults are faceless and they are clumped up together, there is a lot more dialog from them that Serafina overhears.
Like most younger fiction, the few people she does tell about this black cloaked man don't believe her or don't believe her suspicions about the person she believes he is. She is all on her own to save the day. I, personally, don't really care too much for this. She does get a help from an unexpected source, the the reasoning behind this source was more fantastic (full of fantasy elements) than was hinted at. I think there needed to be a little more foreshadowing on the "creature of the night" that she is instead of the quick wrap up that left me hanging more than I wanted to. We believe these characters talk afterward and more of an explanation is given, but we, the reader, don't get that. Foreshadowing or flashes to another POV or some type of mythology about these "creatures of the night" would have been more helpful and more believable to me.
Serafina as a character I thought was intriguing, though some of the other characters seemed faceless to me (as well as a lack of description in the setting). There was a lot of third person narrative from her viewpoint and her thought process which was done well and accurately.
I probably won't pick it up to read it again. I may recommend it to younger kids, but not very many adults even though it has an interesting concept.