In the novel Sad Cypress, Jessie Hopkins is a district nurse sometimes helping nurse O'Brien taking care of Mrs Laura Welman.
Nurse Hopkins is described as being a "homely-looking middle-aged woman with a capable air and a brisk manner". She is also described as having a long nose.
According to Dr Lord, Nurse Hopkins is a "sensible, shrewd, middle-aged woman, quite kindly and competent, but a sight too much interested in other people's business".
On the day Mrs Welman is found dead, Nurse Hopkins is unable to find a tube of morphine that had been in her attaché case, which she had brought to Hunterbury. She is unable to find it at home, and tells Nurse O'Brien that it must have accidentally fallen into the wastepaper basket.
Nurse Hopkins advises Mary Gerrard to make a will, and also advises her on what to put down, so that in the event of her death, her money would go to Mary Riley, her mother's sister.
Nurse Hopkins finds out from Mrs Slattery about the relationship betwee Mrs Welman and Sir Lewis Rycroft.
After the death of Mary's father, Bob Gerrard, Mary returns to Maidensford to attend the funeral, and Nurse Hopkins puts her up. She also helps Mary clear out her father's things from the lodge at Hunterbury.
On the afternoon of Mary's death, Nurse Hopkins had made tea, and Mary had poured it out. She also told Elinor that she had pricked herself on a thorn from the rose trellis at the lodge.
When Poirot interviews Nurse Hopkins after Mary's death, she tells him that Bob Gerrard had told her that Mary was not his biological daughter. However, she says that she may or may not know who Mary's real father was, and that she will not say anything more.
Nurse Hopkins later shows Poirot a letter in which Mary's mother revealed that Mary was actually the biological daughter of Mrs Welman and Sir Lewis Rycroft.
Nurse Hopkins testifies during Elinor Carlisle's trial. She states that she lives at Rose Cottage, Hunterbury. She tells the court about the tube of morphine which had been missing from her attaché case, as well as details of the day of Mary's death.
Later it turns out that nurse Hopkins actually is Mary Riley, the sister of Eliza Gerrard (Mary Gerrard's mother). Mary Riley had moved to New Zealand, and her married name is Mary Draper. She travelled back to England using the name Jessie Hopkins.
It is revealed that the police of New Zealand had been watching Mary Draper for some time, although they were unable to get sufficient evidence for a conviction. An elderly patient had left her a legacy, and this patient's death had been a puzzle to the attending doctor. Mary Draper's husband had also died suddenly and unaccountably, after insuring his life in her favour.