The Prisoner in the Castle is Susan Elia MacNeal’s latest Maggie Hope mystery, with a plot that owes more than a little to Agatha Christie.   Maggie has been posted to  Killoch Castle, a  lodge in the Hebrides. She is there along with other agents with  knowledge too sensitive to leave in the field.  When one by one, the guests begin to be murdered, Maggie must discover who the killer is if she is to survive.    MacNeal’s latest is “darkly atmospheric and as beautifully woven as a clan tartan” (Lauren Willig).