Compare Mary Reilly by Valerie Martin to The Strange case of Dr Jekyll and Mr Hyde by Robert Louis Stevenson.
The Strange case of Dr Jekyll and Mr Hyde is the well-known and often repeated tale by Robert Louis Stevenson. Even the term "Jekyll and Hyde" is a documented colloquialism to describe a person with two extremes of temperament; whose personality is both pleasant and, when provoked, may be the epitome of evil. It is told from a third person perspective, expressing the opinions of Mr Utterson, who is Jekyll's lawyer, trying to understand the "murderous mixture of timidity and boldness," that Hyde represents to Utterson. This is interspersed by contributions from Mr Enfield, Jekyll's distant cousin and later by Dr Lanyon and even a letter (read posthumously) from Jekyll himself to Utterson.
Mary Reilly, by Valerie Martin, tells the story of Mary Reilly, a housemaid in Dr Jekyll's home. Mary feels secure in Dr Jekyll's home, after an abusive upbringing, but is constantly usurped by Mr Hyde. The novel is written as Mary's diary entries and is written to complement Stevenson's original book with genuine historical facts present in both. However, as it is told from Mary's perspective, some of the character representations differ. Valerie Martin's version, whilst true to Stevenson's story, also gives a more feminine outlook to Jekyll and Hyde; something which is missing from Stevenson's version as Jekyll associates with male friends. Mary is also, as a housemaid, representative of a different class in notoriously class-conscious England of the nineteenth century. Mary visits an impoverished London neighborhood and is unwittingly complicit in Mr Hyde's deeds as Mrs Faraday tells Mary that Dr Jekyll has unleashed "his bloody favorite (he has) set loose among us here like a mad dog." In Stevenson's version, the unnamed housemaid is mentioned only once.
In Stevenson's book, the doctor is described as having once been a kindly man who "began to go wrong, wrong in mind..." and his transformation is linked to his obsession with scientific experiments whereas, in Mary Reilly, Jekyll's health suffers as a result of his scientific obsessions. His health issues are more prominent. Even as Mary begins to understand more of Jekyll's situation and his connection to Hyde, she remains devoted. Both Stevenson's book and Martin's version explore the evil in everyone and the potential for the dark side of a person's nature to take over his or her personality.