Fiona Mountain, Oxfordshire novelist and mother of four, says books are her passion. She loves both reading and writing them and is never happier than when she is standing in a bookshop, relaxing with a book at the end of the day, or facing a blank sheet of paper.

Perhaps she would have written her first novel much earlier if she hadn’t been equally passionate about her first job as press officer at BBC Radio One. She spent ten years with the BBC before she had enough courage to give up her dream job in London, so that her urge to write could be given its head.

Now she lives in the heart of the Cotswolds and has four novels to her name, none of which would have been possible without her overwhelming need to write and keep writing. She admits that while she is writing, her characters become her friends and at times she spends longer with them than with her family.

Her latest book, Lady of the Butterflies, is about a real 17th-century naturalist, Lady Eleanor Glanville, who was working at a time when it was unusual for anyone, let alone a woman, to pursue entomology.

She is the first and only person to have a butterfly named after her. The Glanville Fritillary is now found only on the Isle of Wight, and is threatened by modern agriculture and climate change.

Fiona has turned Eleanor’s story, set in Somerset and London during the turbulent time of the Restoration, into a dramatic tale of passion, prejudice and death by poison, of riot and rebellion, science and superstition, madness and metamorphosis It is also about the beauty of butterflies, hope, transformation and redemption. Her heroine is the daughter of a strict puritan and Roundhead major living in a medieval manor on the bleak Somerset wetlands. Eleanor’s longing for colour and brightness leads to an obsession with butterflies as well as to an illicit passion for the charismatic but troubled Richard Glanville, son of an exiled cavalier, who embodies all that Eleanor has been told to despise and distrust. The only peace she can find is in her long-lasting friendship with renowned naturalist James Petiver, a clever young London apothecary who is credited as the father of British entomology.

Fiona chose Eleanor as the subject for her fourth novel as she admired her passion, obsession and overwhelming interest in butterflies. The fact Eleanor was a woman struggling against a man’s world intrigued her too.

She writes nothing until her research is done. This usually takes at least a year.

“Once I am sure I have gleaned all the information I can, I begin planning out the chapters. I then write down exactly what I want to happen, but in a very cold formal way that includes all the historical facts, including small details such as the food they would be eating.

“I then put my notes to one side and begin writing all over again. At this point the main work is done and I can start enjoying myself.”

Fiona describes the first draft as a sketch. “It’s like painting a picture, which has to be outlined in pencil first. The second draft is where I add the colour and the flourishes that are so necessary if I am to breathe life into the characters. This is the point where they begin to take over my life,” she said.

Authors seldom get involved with choosing the cover of their book – this is usually left to the publisher, but as Fiona has built up such a good relationship with her editor, she was allowed to make suggestions. Perhaps this is why the cover, which depicts Eleanor set against the wild landscape she loved so much, is so colourful and evokes the period so dramatically. Fiona explains: “Together, we picked the dress, finally finding the right one, which was both opulent and beautiful, at Angels Costumiers.

“We then selected a model and a photographer. I was even allowed to help choose the gold trim that goes round the edges of the cover rather like a picture frame and sets the whole scene off. That was all very satisfying,” she said.

Fiona is now working on her fifth novel, based on the life of Charles I’s queen, Henrietta Maria.

l Lady of the Butterflies is published by Preface at £11.99.