Agatha's wrong address mystery

Agatha Christie's most confounding mysteries were often solved by Hercule Poirot and Miss Marple. However it has taken a softly-spoken historian from English Heritage to unravel the queen of crimewriting's final conundrum - and prevent the blue plaque mounted in her honour today being placed on a house Christie never inhabited.

Emily Cole, EH's Blue Plaque Historian, has uncovered evidence that proves Christie lived at 58 Sheffield Terrace, Kensington - not number 48, the address Christie wrote in her autobiography and the spot to where her fans make their pilgrimages.

When the job of researching which of Christie's various addresses deserved the plaque first landed on her desk, Emily Cole thought it would be a case just like any other.

"Agatha Christie had seven major addresses," said Ms Cole from her offices in Savile Row. "She loved houses, they were one of her passions."

Ms Cole consulted Christie's autobiography to determine which of these addresses was the most important in her personal and professional history. She soon settled on the house in Sheffield Terrace, where the author lived between 1934 and 1941 with her second husband, archaeologist Max Mallowan.

It was the obvious choice for three reasons. Firstly, it was the only one where Christie had a dedicated writing room. Secondly, the books she wrote in that room are amongst her most famous, including Murder on the Orient Express, The ABC Murders and Death on the Nile.

Finally, her time at "48 Sheffield Terrace" was, Christie recalled, one of the most "satisfying" and "carefree" of her life. "It was a happy house," she wrote.

It was only when Ms Cole visited Number 48 she realised something didn't quite add up: "Number 48 is a lovely house - perfect for a blue plaque - but I realised Christie's description of the house she lived in didn't tally with the house I had seen.

"She describes going into the hall and up a staircase off which there was a room on the left and a room on the right. But Number 48 is a classic terraced house - with the stairs on one side and all the rooms on the other. That is when my curiosity was aroused."

Suddenly the possibility arose that any of Christie's millions of devotees around the world who were drawn on a pilgrimage to 48 Sheffield Terrace had visited entirely the wrong house.

It took a visit to the London Metropolitan Archives and plenty of patient searching for Ms Cole to find indisputable evidence that proved her hunch was right - electoral registers showed Christie lived at number 58, not number 48.

A return visit to Sheffield Terrace clinched the case. Number 58 is a handsome detached house with a central staircase - just as Christie had described.

The case was closed - and today, thanks to Ms Cole's sleuthing, the blue plaque in Christie's honour will be mounted where it should be.

"It is very satisfying indeed, because I know I have been thorough and done my job," said Ms Cole: "Part of my job description is detective work and badgering around in archives - when you discover something unknown like this it is a wonderful feeling."

The one remaining loose end is, of course, just why the Christie got her own address wrong.

It could have been because Christie was 75 when she wrote her memoirs and had lived at two houses in her life numbered 48.

The other, intriguing, possibility is that her error was deliberate - one final Agatha Christie mystery.