Actually, it’s not much of a mystery. It was probably cancelled because of poor sales, same as any other book series that gets pulled. The books evidently never reached the success of the likes of Fear Street or Christopher Pike, and they get progressively worse in quality; switching focus from OK-ish teen horror to what is basically glorified abusive romance with some pseudo-astrology thrown in. Maybe Zodiac Chillers hit the market at the wrong time – they were published towards the tail-end of the YA horror boom, but too early for the supernatural romance wave popularised by Twilight.
According to a notice inside the final book (Pisces Drowning), there were supposed to be thirteen Zodiac Chillers in total. If the full series had been published, we would have got:
- Rage of Aquarius
- The Scorpio Society
- In Leo’s Lair
- Twisted Taurus
- Never Love a Libra
- Pisces Drowning
- The Thirteenth Sign
- Virgo’s Vengeance
- Gemini Divided
- Claws of Cancer
- Psycho Sagittarius
- To Kill a Capricorn
- The Aries Oracle
There are entries for #7 and #8 on Amazon.com but it seems they were never published. We do get summaries though:
The Thirteenth Sign by Ellen Steiber – “Learning on her thirteenth birthday that she is adopted and that no one knows what day her actual birthday is, Camellia confides in her friend Tom and learns that he is an emissary from an advanced alien civilization of healers.”
Well, this definitely sounds more interesting than any of the books that actually made it into print. Aliens, and a younger protagonist, bring the refreshing promise of something different. The title suggests that the book would have focused on Ophiuchus, an apocryphal “thirteenth sign” of the zodiac.
Virgo’s Vengeance by Ruth Koeppel – “Judy, a cautious Virgo, becomes obsessed with her boyfriend, Kyle, and will do anything to keep him, even when he sets his sights on another girl.”
This does not sound refreshingly different, and seems like it would have been pretty much a repeat of Twisted Taurus / In Leo’s Lair. Koeppel did not write any of the existing books, so I don’t know whether she would have done a better job with this storyline. Given that most of her listed bibliography is cringey TV tie-ins for kid’s TV shows, I’m willing to bet the answer is “no.”
I can’t find out any more on the other books, but several of the titles suggest they too would have been variations on the theme of “jealous/obsessed person stalks love interest and kills anyone they see as a rival.” So perhaps it’s just as well Pisces Drowning was the last one.