St. Paul's Hidden Falls, "where people sometimes shed their clothes along with their inhibitions," may seem a far cry from Seal Harbor, Ireland, but in Erin Hart's deeply romantic and lyrical novel, "False Mermaid" (on sale Tuesday), the third in her acclaimed series featuring pathologist Nora Gavin, the two are as linked as a selkie to her skin. The myth of the selkie is as common in Celtic cultures as fine whiskey, coarse wool, fiddle music, the gift of the gab, and a deep melancholy that shades a Celt's soul. According to the ancient myth, the selkie is an enchanted seal with the ability to shed her skin and take human form. The person, usually a man, who possesses the selkie's skin possesses the woman. Only when the selkie reclaims her skin, can she regain "her true self." In Hart's novel, the selkie myth serves not only as an elegant plot device, weaving the 19th-century story of the disappearance of a fisherman's wife in County Donegal with the 20th-century murder of Nora's sister, Tríona, in St. Paul, but the myth also becomes a symbol for the besieged selves and complex identities that lie beneath Hart's characters' skins. From minor characters like the haunted Cambodian refugee fishing beneath the falls who dreams of going to medical school to Hart's main characters -- Nora and her Irish lover, Cormac Maguire -- each one struggles with his or her "impossible dualities."

In Hart's debut, "Haunted Ground," Nora fled Minnesota for the bogs of Ireland to escape her sister's unsolved murder. She can no longer live with that choice or with the possibility that her ex-brother-in-law, whom she believes killed her sister, may be about to marry and murder again. Nora leaves Ireland, abandoning Cormac to sort out his own troubled past, and begins a quest to save her niece and make a case against her sister's husband.

For all its evocative descriptions (the bluffs of the Mississippi as much as the coves of Donegal) and its captivating characters, the plot has flaws. None of them cut into the novel's lush romanticism, but they do disrupt its suspense. Significant discoveries that propel the mystery forward are contrived and stretch credibility. For example, Nora discovers clues to her sister's murder that, given their placement and Nora's close relationship with Tríona, should have been discovered within days of Tríona's death -- and if Nora didn't find them five years ago, her police detective confidant then and now, Frank Cordova, certainly should have.

Nora also swoons too frequently and has a few too many sighing internal monologues; however, these narrative stumbles are easily ignored as the story races to a breathless confrontation on the headland of Port na Ron and the shocking realization of what a person might do to protect her skin and that of someone she loves.

Carole E. Barrowman teaches at Alverno College in Milwaukee and blogs at carolebarrowman.com.