Miss Miranda Dennison is not pleased to be sent to visit her sister Rosalind instead of accompanying her parents to Italy. Rosalind lives with her new husband Philip in an isolated Abbey near the coast in Northumberland. Miranda expects a dull time, but she does not expect to find her sister being kept a virtual prisoner by her husband. In place of the charming young man who courted Rosalind during her Season, there is now a brooding stranger.
Miranda is determined to get to the bottom of things, and she is joined in her investigation by a fellow houseguest, Philip's cousin Alan Creighton. Eventually Miranda learns the real reason for Rosalind's reclusive behavior and, more importantly, discovers that a group of unsavory Londoners have infiltrated the local smuggling operation. But when Alan shares the information she discovered with Philip without reciprocating, Miranda decides she must go it alone.