Peggy Couper only knew part of the story about why her mother was adopted at the age of four.

That was until she stumbled upon letters written almost 100 years ago, which shone a new light on the heartache that had surrounded her grandfather’s decision.

The letters led Mrs Couper to take a personal journey of discovery as she pieced together her family story and met 16 first cousins who had never been part of her life.

She has written a book about that journey, entitled Deborah’s Letters, which is launched in Bermuda today.

Mrs Couper’s mother Deborah died in 2010, and it was as she was clearing items from her late mother’s home that she was handed a drawer of personal items, which included a safe. Inside the safe were letters written by her biological grandfather to the family who adopted and raised Deborah from the age of four.

“I sat at home, read the letters and wept,” said Mrs Couper. She had finally discovered the full story of why her grandfather had given up his six young daughters — including her mother.

Up to that point all she knew of her biological grandfather, George Matthew, was what she had been told by her mother. But her mother had never spoken in great detail about the circumstances that led to the sisters being raised by adoptive families.

Mrs Couper held an unfavourable view of her biological grandfather, but all that changed when she opened the safe and read his letters.

The death of Mr Matthew’s wife in 1919 from the Spanish flu pandemic, which killed tens of millions around the world, led to the family being torn apart. He was living and working as a teacher in New York state at the time. There were offers of help to raise the six young girls, and ultimately that was what happened.

Mrs Couper’s mother had no contact with her real family until she was contacted by her younger sister when she was 18.

Through her mother Mrs Couper had learned some of the stories about how the family was split up. But, as she writes in her book, she had always given her grandfather “zero out of 10 for ditching his six little girls”.

The letters were written by her grandfather to her adoptive grandparents, and had been placed in an envelope to be given to Mrs Couper’s mother “sometime”. They revealed his heartache at parting with his children.

“My grandfather was devastated. That got me thinking ‘this man is not a bad man at all’. It changed all my feelings.”

The revelation was the start of a journey to discover more about her roots, tracing her extended family and meeting more than a dozen first cousins she had not been unaware of.

“It was thrilling to get in touch with them,” she said.

After attending a writer’s retreat with author Jan Fraser, Mrs Couper spent 18 months writing the book Deborah’s Letters, with additional guidance from editor Rosemary Jones.

The book tells the story of her journey of discovery as she traces the story of her mother and her five sisters, and her biological grandparents George and Alice Matthew.

The book was launched in Canada earlier this year and has found favour in New Brunswick, where Mrs Couper’s great grandfather George F Matthew was a founding father of the New Brunswick Museum.

Mrs Couper was one of Bermuda’s top female road runners in the 1980s, and her daughter Ashley Estwanik is a multi-May 24 women’s champion.

When asked how the discovery of the letters and tracing her family roots has impacted her, Mrs Couper said: “It was not that I felt I was missing anything, but now I feel complete.”

• Deborah’s Letters will be launched in Bermuda at 5.30pm today at Masterworks, in the Botanical Gardens.

The book will subsequently be put on sale at Masterworks.