I delved into my family's history – and discovered a long-hidden secret. But was it mine to tell? | Marisa Bate

I'm sitting in my great-aunt's retirement home on the outskirts of Detroit, Michigan. It's not yet October, but for reasons I don't quite understand the home is throwing a Thanksgiving dinner for residents and guests. I join my great-aunt June and the other octogenarians piling up their paper plates at the buffet. Then we sit at trestle tables lined with tiny pumpkins, while framed photos of the recently deceased sit on top of the grand piano, seemingly looking our way.

The early holiday celebrations weren't the only surprise when I arrived in Michigan. I was there to research a book I was writing about the history of the women's movement, but also about my mother, whose life story echoes the rise and fall of second-wave feminism. In 1974, a year after Roe v Wade passed, my 22-year-old mother travelled from Essex, England to New York City and took a Greyhound bus across the country to visit June, who was then living in Omaha, Nebraska. At that time, my mum's life, as it was for so many women of the era, was full of promise. She was the first in the family to go to university, coming of age alongside the revolutionary ideas of the 1960s. I wanted to learn from June who my mum was when everything still seemed possible. I was on this journey as a journalist and as a daughter; in each of these roles, I wanted to know everything.

June is my grandfather's sister. It was on my trip, a recreation of the same one my mother made in 1974, complete with a Greyhound bus ride across the midwest, that, at the age of 35, I finally saw his face. He was a violent bully of a man who died some years ago, whom my mother had never allowed me to meet, not that I had any desire to. Cousins have shown me pictures of him and my grandmother where his face is always scribbled out. But on the wall of June's apartment, there he was.

I knew the story of my grandfather well. Or so I thought, until over slices of turkey, one of June's children, Terry, who had joined us for the Thanksgiving lunch, asked me how Paul* is. "Who's Paul?" I asked. Terry looked at June. June looked at me. I knew my grandfather left my grandmother, but I didn't know, until that moment, that he had a second family and my mum had a half-brother, Paul, living in England. June was keen for me to connect with him. I texted my mum. "I probably just forgot to mention it," she replied.

I'd travelled a long way in search of a greater understanding of my mother and here was a compelling lead – a whole new family, who, judging from what I could decipher from Terry and June, had a very different relationship with my grandfather.

A few weeks after returning to the UK I received a Facebook friend request. I'd hit the journalist's jackpot – Paul wanted to connect. I was itching to unearth the story of my mother from a new perspective, one I didn't know existed. New branches of a family tree were appearing in real time, pointing like arrows I should be following.

Everything is copy, Nora Ephron said, and the writer in me felt this throb in my fingers. But in this moment, I was confronted with a much thornier notion of storytelling. Who owns this story? I had inherited it, but not entirely. A story isn't like a necklace – something only one family member can wear at a time. The story is a part of who my mother and her siblings still are. It is ongoing. Its passing down is still in transit, still in the present tense, and there are multiple hands this story passes through before it gets to me. As a journalist, discovering Paul felt like it was "my" story. Yet as a daughter and a niece, it felt like a betrayal. What right did I have to expose a wound kept out of the daylight for decades?

And so I didn't follow my lead. The Facebook friend request remains unaccepted, and that arm of my investigation came to a close. The daughter in me won out – I realised it was no longer my story to follow. I haven't stopped believing in the power of storytelling, but I have re-evaluated who can be the storyteller. I have thought harder about the stories that we use to understand others, and I have a newfound respect for – and acceptance of – what is not mine to know. The pursuit of truth can't feel like breaking and entering, even if a door has been left open. This story may have been only a click away, but just because something is in easy reach doesn't mean it's yours for the taking.

Marisa Bate is a journalist, author and former Guardian reporter