|Hodder & Stoughton, 1978|
|Knight, paperback, 1978|
|Red Fox, 2001|
Black Nightshade was first published as part of Black Beauty's Family in 1978. The other stories were: Black Romany (Diana) and Blossom (Christine). Black Nightshade was published as an individual volume in paperback by Knight in 1978. That was its only appearance as a single story. It has had at least two more outings, published by Chancellor in 1986 as Black Beauty's Family, with the stories in the original collection and a further three; and as More from Black Beauty's Family in a paperback edition from Red Fox in 2001, this time containing the original three stories.
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Josephine Pullein-Thompson has a full section on my site, including an interview. For more on the complicated publishing history of Black Beauty's Family, there's a section on that, too.