(Years ago, when I read Angelique's Descent, it got me thinking about the kind of “master narrative” I'd have cooked up to tie together elements of the backstory. I present this without any real tinkering. I'd handle it differently now. So, I just present this as a bit f my own backstory-thinking from a different time and place in my life. This is lifted from an old email to an old friend.)
Only at the end of the TV series do we learn that Angelique is the reincarnation of the 1690's witch, Miranda DuVal. She was mixed up with warlock Judah Zachary and ratted on him. It can be assumed that his curse is largely the reason that Collinsport was so screwed up for centuries to come, right up to manipulating the ghost of Gerard Stiles in the show's penultimate storyline.
So, logically, my version of Angelique's story begins in the early 1790's when she realizes the power in her reincarnative DNA. She's an orphan in her late teens when a guy shows up claiming to be her brother. It's Nicholas Blair. He tells her of her power and helps her to use it. But he tries to use her power in a ritual in such a way that she realizes it'll burn her out, kill her. A ritual involving the Leviathans. She gets hurt enough that she becomes determined to protect herself, even if it means using evil means to do so. Fearing her life from a pursuing Blair, she goes on the lam. She needs to develop her sorcery in secret, and post-Inquisition Europe is not that place. She also needs to develop a kind of sorcery that will be unfamiliar to Nicholas Blair or the Leviathans. She adopts the identity of a French maid and high-tails it to Martinique. A good place to hide and study voodoo.
Naturally, she's totally mistrustful of men. But she meets Barnabas. A painfully shy guy who seems too old to be unmarried. Barnabas kinda loves Josette, but it's all an arranged marriage coming up. Angelique can't help but fall for the guy, who is the exact opposite of Nicholas Blair and all of the other men who would mistreat a comely orphan. He's an almost-middle-aged Hamlet, with a craggy intensity mixed with a gentle melancholy. An emo father figure. They hook up. She thinks she might be able to give up sorcery and live in peace and quiet. Barnabas freaks out because he actually feels love, and this makes him completely vulnerable. He sees Josette as someone very safe, and convinces himself he loves her.
Blair shows up and puts the whammy on Barnabas, seeing this as Angelique's vulnerability. He threatens to kill Barnabas (who, being whammy-ized, will have no memory of this) if Angelique doesn't join him and the Leviathans. But Angelique's been practicing, and fights back. She destroys (so she thinks) the Leviathans. The only way Blair can save his essence is by committing his eternal soul to Diabolos, another of the Great Old Ones, as he dies.
Barnabas, slowly coming out of whammy, confesses his love for Angelique before the whammy wears off. When he fully comes to, he has no memory of this and goes off to Josette. Angelique follows them to Collinsport with an optimism that Barnabas might be turned around. A curious Barnabas finds an odd, small wooden box in Martinique, which he takes back as a keepsake. It vanishes on the voyage, only to show up many years later as the Leviathan's Naga Box.
This is a pretty simple story. It just takes all of the loose ends of DARK SHADOWS and makes them make sense. Loose ends such as Miranda DuVal's reincarnation as Angelique. Nicholas showing up in the 1960's and claiming to be Cassandra's (aka Angelique's) “brother.” Nicholas' servitude to Diabolos (their euphemistic name for Satan) that sort of gets mixed up with the Leviathans. Oh yeah, the whole Leviathans thing gets pulled in. And it makes sense why Angelique keeps this weird hope for Barnabas. And, when Angelique takes that bullet for Barnabas in 1841, it's no longer a non-sequitur when Barnabas suddenly announces his love for her in her death throes.