Mistress of Mellyn is both a romance, in its concentration on the slowly-developing love of Martha and Connan, and a mystery, or series of mysteries.

As with the lovers in Shakespeare's romances, these lovers meet with ambivalence, spar, and must overcome great obstacles before reaching their happy ending. The mystery is intertwined with the love story, placing doubts in their paths, doubts about character and culpability. If Connan's wife left him for another, perhaps he drove her to it with his philandering.

Lord Treslyn's conveniently-timed death raises the suspicion that Connan and Lady Treslyn, who have been lovers, are not only cruelly toying with Martha, but are guilty of murder. All of these signs and suspicions must be sorted out before the lovers can reach a true understanding. As each new question or new mystery arises, it appears to be an obstacle. In retrospect, each obstacle is shown...