This film was shot concurrently with the original Dark Shadows (1966) series. During the time of filming, the television program was in the middle of its 1970 parallel time story-arc. Major characters appearing in the film were written out of the TV series so that they would be available to shoot the movie.
Scenes that were scripted but never filmed involved a Collinsport resident named Nancy Hodiak meeting Jeff and Maggie at Jeff's cottage to pick up a painting that Jeff had painted of her. As Nancy leaves the house, she is stalked and killed by Barnabas. Many elements of Nancy's attack scene were used in the final cut in the scene of Barnabas attacking Daphne. Had these scenes been included in the film, Marie Wallace would have played Nancy.
"House of Dark Shadows" was filmed concurrently with the original Dark Shadows television series. During the time of filming, actors were written out of the TV series so that they would be available to shoot the movie. Kathryn Leigh Scott was absent from 30 episodes (986 to 1015); Jonathan Frid was absent from 28 episodes (983 to 1010); Grayson Hall was absent from 21 episodes (986 to 1006); John Karlen was absent from 21 episodes (990 to 1010); Nancy Barrett was absent from 20 episodes (991 to 1010): Louis Edmonds was absent from 17 episodes (991 to 1008); Don Briscoe was absent from 15 episodes (986 to 1000); Joan Bennett was absent from 15 episodes (991 to 1006); and David Henesy was absent from 9 episodes (993 to 1001).
The trivia item below may give away important plot points.
This movie is an adaptation and re-imagining of the major storylines that ran throughout the 1967 season of Dark Shadows (1966): Barnabas is released by Willie, he attempts to woo Maggie, Dr Hoffman arrives and develops an obsession with Barnabas.