In The First Joanna Dorothy Blewett explores Australia's acceptance of its convict heritage, tracing the fictional history of the Deverons, owners of a leading South Australian vineyard. The property, situated near the Onkaparinga River, was established in the early years of the colony by settler Stephen Deveron. The central characters of the play are the Joanna Millay, a young convict woman who becomes the matriarch of the Deverons, and Joanna Deveron, the wife of the second Stephen Deveron - the grandson of the first Joanna and the first Stephen Deveron.

The narrative begins on Joanna's birthday in 1945 and introduces the Deveron family. Joanna has only recently arrived at the vineyard and is still suffering from the effects of several years spent as a prisoner of war in Poland. Joanna and Stephen had married in England shortly before the outbreak of war but were forced apart after she became trapped behind enemy lines. Having led a peripatetic upbringing in Europe Joanna finds the dull monotony of life on the vineyard unbearable and is thinking of returning to Europe. Her love of Stephen is making the decision all the more painful.

When Stephen's maiden aunts give her a chair belonging to their mother, Joanna is at first horrifed by the thought of its staid existence. She at first can't bear think about it, but after discovering within the chair a set of diaries written by the first Joanna she becomes fascinated. The diaries reveal a life of trauma, loss, murder, illegitimacy, and eventually, triumph through love. Through her reading of the diaries the play's dramatic action segues into "interpolated scenes" depicting key moments in the lives of Stephen's forebears during the nineteenth century - 1837, 1849, 1862, 1871, and 1885. The diaries ultimately allow the contemporary Joanna the capacity to imagine a future at the vineyard with the man she truly loves.

Characters in the play (in order of appearance):

• 1945: Stephen Deveron, Mrs Collins (who “obliges” at Chateau Deveron), Joanna Deveron, Jocelyn Cuming (Stephen’s second cousin), Halley van Druyten (Captain in the United States Army), Editha and Viola Deveron (Stephen’s twin great-aunts, aged 92), Jackson (the chauffeur)

• 1837: Sir Bertram Tavener (Governor of a women's jail in Tasmania), Lady Caroline Tavenor (his wife), Miss Beatrice Tavenor (his sister), Captain Jules Smith (of the British Army, aged 29), Stephen Deveron (1st, aged 22), Joanna Millay (the first Joanna, aged 17).

• 1849: Stephen (aged 34), Joanna (29)

• 1862: Joanna (42), Stephen (47), their children: Augusta (20), Phillip (14), Editha and Viola (10); Major Jules Smith (54)

• 1871: Viola and Edith (18), Joanna (51)

• 1885: Joanna (64), Stephen (69)