Karen Knowles is an Unexpected Guest at the opening of author Agatha Christie’s summer home in Devon

The Devon home where crime fiction writer Agatha Christie spent her summers and entertained guests with readings from her thrillers, is a national treasure.

Greenway, near Dartmouth, has a marvellously lived-in, old fashioned feel, with hats on stands and personal belongings everywhere.

There are no ropes or barriers; it is almost as if the family popped out and forgot to lock the door all those years ago. For the National Trust has returned Greenway to its 1950s heyday, and the result is as though time has stood still.

The Grand Dame of Mystery bought Greenway in 1938 and regularly spent summers there with her second husband Max Mallowan.

In 1959 Rosalind Hicks, Christie’s daughter, and her second husband Anthony Hicks took over Greenway, eventually giving it to the National Trust in 2000, while they still lived there. But it was in 2006, shortly after their deaths, that Christie’s grandson Mathew Prichard, decided to donate most of the contents as well.

In February this year, Greenway opened its doors to the public for the first time. It had taken two years of volunteers, builders, curators, conservators and craftsmen working around the clock to recreate what Christie described as “the loveliest place in the world”.

Greenway was the perfect retreat for the famous author, secluded, surrounded by woodland and overlooking the River Dart. As a result parking is extremely limited, access roads are narrow and, with more than 600 people a day expected in the summer, visitors are being urged to find an alternative to using their cars.

Our first glimpse of Greenway was from the ferry, which operates from Dartmouth several times a day. It takes just 20 minutes to reach the tiny quay opposite the pretty village of Dittisham.

After a five-minute uphill walk, we arrived at the Georgian property and entered as the family would have done: via the kitchen.

As we moved around the house, we saw the drawing room with Agatha Christie’s grand piano. Apparently she was a talented player, but far too shy to play in front of family or guests. This was also the room where friends and family would gather to hear Christie read from her latest manuscript and then try to guess whodunnit.

As the tale goes, her husband Max would often awake from his doze to announce the name of the murderer – much to Christie’s annoyance.

As we moved to the library, a surprisingly poignant blue and white mural, painted by an American officer during the Second World War, caught our attention.

Greenway had been requisitioned by the Admiralty for the use of the United States Navy. As part of the preparations for D-Day, Greenway became the officers’ mess for the 10th US Patrol Boat Flotilla based in the Dart Estuary.

Among them was a Lt Marshall Lee, who was to become their unofficial war artist. It was he who created the frieze around the walls of the library. When the serviceman left, Christie wanted it kept as a memorial.

And it fits perfectly in a house where each member of the family was obsessed with collecting. As a result, items range from the rare and extremely valuable to the distinctly odd. As we looked at the gorgeous views of the River Dart from Christie’s former bedroom, I overheard a visitor say: “It feels so real, it’s almost spooky. You almost feel part of a real life murder mystery, waiting for the killer to strike.”

For the ultimate thrill, diehard fans can take the experience to another level. One floor of the main house has been turned into a five-bedroom holiday apartment, sleeping 10. The cost for a week in high season is a cool £2,400.

* Cars won’t be admitted without prior booking. Visitors arriving by “green transport” get a discount. For the river link, tel Quay & Ferry Services 01803 844010, www.greenwayferry.co.uk