When her fiancé walks out over a painting, dated 1890, of a girl bearing a striking resemblance to her, a gifted jeweller with an innate sense of the mystical but a latent fear of abandonment determines to return a precious brooch to the past through a geometric portal she's found that responds to energetics and sound so she can put right an old injustice and save herself and the man she loves from ruin; but a malicious and vindictive suitor stands in her way just as one did a hundred years ago.

A Harp of Truest Tone is an historical novel about a contemporary woman living in Melbourne, Australia, who experiences memories of her ancestor's life and love for a convict who escaped Western Australia in the 1860s and sailed to Boston. Unravelling and healing the injustice that happened to her ancestor, she finds herself fighting for her own true love.

Lesley Seymour designs a harp shaped brooch after experiencing a series of dreams – really ancestral memories - and sees a photograph of a young convict, John Boyle O'Reilly. Recently split from her fiancé Cameron Donne, she becomes immersed in unravelling the connection between the memories and the convict; in so doing, she discovers a geometric portal that takes her back to her ancestor Ally O'Leary's time.

When competitors in the industry reveal a new jewellery range based on the harp shaped brooch, and claim it as a family heirloom, Lesley faces professional ruin and realizes she must return the brooch to the past to heal it and save her own future.

Returning the brooch to Boston 1890, it manifests in Cameron's pocket – Cameron, ancestrally connected to clan O'Reilly- to whom it now belongs. Lesley and Cameron honeymoon in Ireland and decide to stay.