When Helen Dunmore was asked to write a novella by Hammer, a new imprint of creepy fiction, she jumped at the chance, writes Sarah Pitt.

Like her moving novel The Siege, set in 1941 in Leningrad, The Greatcoat is about both love and war, and is written with Helen's usual eloquence and atmosphere. But there's a twist for love interest, handsome Second World War RAF pilot Alec, is in fact a ghost.

In the summer of 1954, newlywed Isabel Carey arrives in a Yorkshire town with her husband Philip. As a GP he spends much of his time working, while Isabel, feeling out-of-place, is alone in their rented flat.

One cold winter night when her husband is out on call, Isabel finds an old RAF greatcoat in the back of a cupboard and lays it over her bed covers to keep warm. Falling asleep, she wakes to hear a knock at her window, and finds herself meeting the intense gaze of a young Air Force pilot, staring at her from outside the window. His name is Alec, and his powerfully haunting presence both disturbs and excites Isabel. As they begin an affair, Isabel starts to question what is real and what is not.

"The idea of the greatcoat came from my own childhood, my father's old RAF greatcoat," says Helen. "My sister and I used to share a double bed and when it was cold we used to put it on the bed at night. I remember how heavy it was. On one occasion a little bit later my sister thought she saw a ghostly figure of an airman at the window. I have never forgotten that."

The story moves seamlessly between the past and present, drawing the reader into the intrigue.

"It needed careful planning for everything to fit together," says Helen.

"I know from my own experience of reading ghost stories that it is very annoying if it doesn't quite hold together, and you think 'I don't believe that'.

"Atmosphere is very important and suspense and the mixture of fear and anticipation you should get from a ghost story, along with a sense of gathering momentum."

It works. This is a story that will get under your skin and make your heart pound.