The Night Digger is a 1971 British thriller film based on the novel Nest in a Fallen Tree by Joy Cowley about two women who are visited by a suspicious handy man. It was adapted by Roald Dahl and starred his then wife Patricia Neal.
 The Night Digger was the American title; it was originally released in the United Kingdom as The Road Builder.
 Maura Prince (Patricia Neal) works part-time as a speech therapist and the rest of her time taking care of her blind, invalid mother, Edith (Pamela Brown). Billy Jarvis (Nicholas Clay) arrives, claiming he was sent there by a neighbor's nephew. He ingratiates himself with Edith, who puts him in Maura's bedroom and claims he must be a long-lost relative. Despite Maura's worries, Billy turns out to be a good worker.
 While attending church with Edith, Billy notices pretty, young nursery school teacher Mary Wingate (Diana Patrick). That night, while having psychotic flashbacks of young girls tormenting him for impotency, Billy goes to her home and murders her, then buries her body at a construction site. She is the seventh victim he's killed. A nurse (Brigit Forsyth) visits Edith and warns that Edith's heart is very bad. Having more psychotic visions, Billy follows the nurse home and murders her as well.
 Edith calls out for Billy. When he doesn't answer, she tries to climb the stairs to his room and has a heart attack. Maura rushes her to the hospital. When Maura returns from the hospital, she almost catches Billy coming home from the murder. To placate her, Billy lies, claiming his mother died in a fire. He weeps, claims he often doesn't know what he is doing, and begs Maura never to betray him.
 The next day, Maura visits Edith at the hospital. Edith demands that Maura throw Billy out, but Maura instead breaks with Edith.
 Maura takes all her savings, buys a new wardrobe, and returns home to tell Billy that she loves him. The two run off to Scotland, where Maura purchases a farm. After some months, Billy meets a young woman who is looking for her dog. Hours later, Billy returns to the farm, psychotic. Maura realizes he has killed again. Realizing he's broken Maura's heart, Billy drives off a cliff on his motorcycle, committing suicide.
 Roald Dahl wrote the script especially for Neal, who was his wife, who was recovering from a stroke that almost killed her. He sent the script to a number of directors including Lindsay Anderson, William Friedkin, Lindsay Russell and Robert Altman. Eventually he went with Alistair Reid, who had worked extensively in theatre and television.
 Patricia Neal later wrote "I received no salary for it. It simply would not have been made had I demanded anything close to my fee. Both Roald and I took expenses only, but would have shared in the profits had there been any."
 Dahl did a deal with Youngstreet Productions who raised money from MGM. The producers insisted the writer fire his attached producer Allen Hodshire. Producer Norman Powell was the son of actor Dick Powell.
 It was the first film for Nicholas Clay after his extensive stage experience.
 Filming started 28 September 1970 and took eight weeks. It mostly took place at Twickenham Studios, in Cornwall, and in an old mansion on the way to Windsor Castle. Neal was accompanied during filming by Valerie Griffith who had helped her recover from the stroke. Neal wrote "It was a very difficult picture for me. Valerie came to help with the lines, but my coworkers did not have the generous spirit of Jack Albertson and Martin Sheen (with whom she had made The Subject Was Roses) and I sensed their impatience when I stumbled. I also remember distinctly, on more than one occasion, hearing them making fun of me. Brain-damaged people can sense when someone is mocking them. We grow antennae."
 The film was a box-office failure. Dahl said "it was so badly made it ran for just a few days in New York and then faded." (Alistair Reid responded "Mr Dahl is a very complicated customer. The director should be the boss on the set. If he was at the beck and call of the scriptwriter life would be intolerable. The script is merely the blueprint for the film."
 Neal wrote the film "brings back hard memories, and I didn't get a nickel for doing it."
 Neal disliked the movie, calling it "pornography." Dahl thought the book was "a fine first novel" but claimed "the director messed that one up... Pat's lovely but the film's a mess."
 Alistair Reid later claimed the film "got very, very good reviews in America and has only been seen in that country. It’s not been shown in this country [England] mainly because Patricia Neal, Roald Dahl and I all took deferred payments which would only come into being if the film opened in this country. So it is actually very much in their interests not to release the film in this country."
 In a contemporary review, The New York Times wrote "It begs for empathy for its tortured principals, but despite the clearly dedicated contributions of Patricia Neal, Roald Dahl...Pamela Brown and a young newcomer, Nicholas Clay, the strain on credibility is a good deal more notable than the impact on the emotions"; Variety praised the acting but called the film "only moderately successful."
 More recently, a reviewer for DVD Talk wrote "The Night Digger doesn't carry much of a reputation, but I found it highly unusual, and more than satisfying." Cinema Retro called it "an underrated gem"; and the Radio Times stated "director Alastair Reid's neo–Grand Guignol chamber piece exudes a peculiar fascination."