In July 2013, I travelled from London to Berlin to visit the lake house my great-grandfather had built. Picking up a rental car at Schönefeld airport, I headed west along the ring road, through Berlin's western suburbs, and into the Brandenburg countryside. Forty minutes after starting my journey, I arrived at the small village of Gross Glienicke, in what had been East Germany.I parked the car and set off for the house. It had been 20 years since I had last visited this place and nothing looked familiar. Although wary of trespassing, I ducked under a strand of barbed wire and pushed my way through a field of shoulder-high grass, heading in the direction of what I guessed was the lake.

To my left stood a row of modern brick houses. To my right stretched an unkempt hedge. And then, there it was, my family's house. It was smaller than I remembered, not much larger than a sports pavilion or double garage, hidden by bushes, vines and trees. Its windows were patched with plywood. The almost flat black roof was cracked and covered with fallen branches. The brick chimneys seemed to be crumbling, close to collapse.

I picked my way round it slowly, touching flaking paintwork and boarded-up doorways, until I found a broken window. Climbing through, my way illuminated by my iPhone, I was confronted by mounds of dirty clothes and soiled cushions, walls covered in graffiti and crawling with mould, smashed appliances and fragments of furniture, rotting floorboards and empty beer bottles. One room looked as if it had been used as a drug den, littered with broken lighters and soot-stained spoons. There was a sadness to the place, the melancholy of a building abandoned.

After a few minutes, I clambered back out of the window and walked towards the house next door, hoping to find someone to speak with. I was lucky, for a woman was working in the garden.

Explaining that I was a member of a family who used to live at the house, I asked what had happened to it? Who owned it now? ''It has been empty for over a decade,'' she told me and then pointed towards the shore. ''The Berlin Wall was built there, between the house and the lake,'' she said. ''It's seen a lot, but it's an eyesore now.''

I had been told about the lake house, or ''Glienicke'', all my life. It had been an obsession for my grandmother, Elsie, who spoke about it with wonder, evoking a time when life had been easy, fun and simple. It had been, she said, her soul place.

My family, the Alexanders, had flourished in the liberal years of 1920s Berlin. Affluent, cosmopolitan Jews, they spent every weekend and most of the summer at Glienicke.

In my mind, I kept an image of the house, compiled from the sepia-tinted photographs I had been shown since childhood: a glistening lake, a wood-panelled room with a fireplace and rocking chair, a manicured lawn, a tennis court. But with the rise of the Nazis, they had been forced to flee, moving to London where they had struggled to establish a new life.

For as long as I can remember, my family had eschewed all things German. We didn't purchase German cars, washing machines or fridges. We holidayed across Europe - in France, Switzerland, Spain, Italy - but never in Germany. The elder generation did not speak of life in Berlin, of the years before the war. It was a closed chapter. Any emotional connection to their lives in the 1920s had been severed. Reluctant to explore the past, they chose instead to focus on their new country, becoming more British than the British, sending their children to the best schools, encouraging them to become doctors, lawyers and accountants.

The next day, I drove to the local government offices in Potsdam, twenty minutes south of the Gross Glienicke. There, in the basement of a municipal building, an elderly woman told me that the lake house was now owned by the city of Potsdam, and that it was soon to be demolished to make way for new homes.

After an 80-year absence, it looked like I had returned just in time to see the house torn down.

Three floors upstairs, I found the historic building preservation department. There I spoke with a young man and woman who were excited to hear about the lake house. They said that I might be able to save it if I could prove that it had significant value - and that its restoration had wide support.

I spent the next two years investigating the story of the house. I learned that five families had lived at the property - a wealthy landowner, a prosperous Jewish physician, a renowned composer, a widower and her children, and a Stasi informant. All had made the house their home, and all - bar one - had been forced out.

I visited archives in London and Hamburg, Berlin and Munich. I spoke with historians, architects, botanists, and politicians - and, most importantly, the house's occupants. In the process, I discovered that the house had been the site of domestic bliss and of contentment, but also of terrible grief and tragedy.

Some of the occupants had made the house their refuge, while others had sought escape from the property. It had weathered storms, fires and abandonment, witnessed violence, betrayals and murders, had withstood the trauma of a world war, and the dividing of a nation.

As I continued, I learned that the house was important, for its story reflected that of Germany over a turbulent century. For, in its own quiet and forgotten way, the house had been on the front line of history - the lives of its inhabitants ripped up and remade again and again, simply because of where they lived.

As I researched, I also worked on the second part of my task: to garner support for the house's protection. When I approached the local community, I was impressed by their willingness to acknowledge the sins of the past and their commitment to help restore the house.

Gaining my family's support proved harder. At a family meeting, one cousin questioned the practicality of renovating a house from England. Another doubted that the building had ever been important to the Alexanders. Then my father said that he ''did not want to put his hand in his pocket…'' I finished his sentence for him ''… when the house had been stolen by the Germans in the first place.''

Feeling mounting disappointment, I started wrapping up the meeting, when one of my younger cousins said that she would willingly help in any way needed. Another said that this project offered an extraordinary opportunity for reconciliation. By the end of the meeting, we had agreed that 14 of us would fly to Berlin and work with the villagers to clean the house. Delighted to now have my family's support, I remained worried. Even if we could pull this off, I wondered, would it be enough to save the house?

Thomas Harding is the author of the bestselling 'Hanns and Rudolf'. 'The House By The Lake' is published by William Heinemann. To find out more about the house visit www.AlexanderHaus.org or follow the author on twitter @thomasharding