The Paperback Library began releasing novels based on the TV series Dark Shadows in December 1966.
All of the novels, with the exception of House of Dark Shadows were part of one shared continuity separate from the history supplied in the original television series.
Most of the books follow a formula of a heroine arriving at, or already living at, Collinwood and falling in love with Barnabas Collins, not realizing that he's a vampire.
The heroine subsequently finds herself endangered by some natural or supernatural threat requiring Barnabas to rescue her.
[1] Many of the 1st printings feature covers with enframed production stills from the television show.