They are solo adventures, much like the Fighting Fantasy books, except they are only about 200 enties long. They are all available online somewhere, if someone can find a link.
They were also turned into a pretty dire computer game.
Quicksilver Fantasies is still trading, but they only deal in music and folkcraft. The writer and original owner of the business (Patricia), a teacher by trade, died in Guam in the early nineties
IIRC.
... And that isn't a First edition Citadel of Fire either.
This week I've been mostly eating . . . chicken and wild rice soup.