Casella Havard is Portland's Harbor Warden. It's her job to protect the city from sea monsters. Of course, being part monster herself can complicate things. Something is changing beneath the waves.

The krabbor are growing bolder, snatching people from the shoreline. If that wasn't enough trouble, Casella gets blackmailed into taking a missing person case, creating a perfect storm for the warden and her best friend, a talking otter named Tenebrae.