Historian Maggie Winegarden decides she needs to spend some time away from her partner Bethany, who is upset over Maggie's desire to be a painter. Maggie visits the seaside town of Hastings and while in St. Clement's Church discovers that poet Christina Rossetti and artist Elizabeth "Lizzie" Siddal had been frequent visitors to Hastings and the church. Agatha, the church caretaker, shows Maggie a chest of papers in the catacombs that the vicar said belonged to Dante Gabriel Rossetti.

Maggie discovers the papers are actually the lost diaries of Christina and Lizzie. She learns that Christina's and Lizzie's lives are intertwined beyond being sisters-in-law, that they become intimate friends and establish a community of women artists and poets, a Pre-Raphaelite Sisterhood in Lizzie's ancestral home, Hope Hall.

Maggie is joined by Bethany and Agatha in the quest to solve the mystery of how the diaries were buried in the St. Clement's Church catacombs and uncover surprising revelations on the origins of Christina's most famous poem "Goblin Market."

Wrapped in a modern-day mystery, The Rossetti Diaries is a historical re-imagining that explores the indomitable artistic aspirations and achievements of the poet Christina Rossetti and the artist Elizabeth Siddal.