What is Lady Flora to do when her twins demand to marry only another set of twins and none are at hand?

When Lady Flora's twin daughters, Clio and Calliope, declare they will marry only twins, she is at a loss on how to proceed. However, her son, James, knows of a pair of young men living in a crumbling castle by the sea. Besotted by the gothic novels they have been reading, the girls could not be happier. An invitation to Castle Blackwater is soon forthcoming. It has everything they desire: hidden passages, an evil lord, and handsome heroes. But, who will marry the heir and which must settle for the spare is entirely another matter.