When a man named Allan Armadale (Senior-1) murders a man named Allan Armadale (Senior-2), it sets in motion a dramatic and long complication that takes twenty years to resolve. By the way, Allen Senior-1 has a son called Allan Armadale (Junior-1), as does Armadale Senior-2 (Armadale Junior-2).
Armadale Junior-1 is told this his father's dying wish was that under no circumstances should he meet up with Junior-2 – believing that Junior-1 will cause some accidental injury to Junior-2. Junior-1 adopts the name of Ozias Midwinter and drops out of society, so luckily, I didn't spend the entire book trying to figure out which Armadale is which (Junior-2 is still called Armadale, by the way).
With me so far?
Since Midwinter spends the first part of his life avoiding contact with Armadale, he gets an interesting upbringing: Vagabond, pirate, gypsy slave, that sort of thing. Armadale knows only a good life under the wing of his father's best friend, a smart priest by the name of Brock.
Of course, the two meet up (otherwise there wouldn't be a story!) and Armadale and Midwinter become best friends pretty much instantly. Actually, In 21st century terms, I'd call it a serious bromance. The two of them don't like to spend much time apart at all.
Midwinter is haunted by visions of inevitable disaster, while at the same time drawn to the simple and foppish Armadale and his quiet life. Armadale, for his own part, suspects nothing. But then Armadale would be surprised by a sunrise every morning. He's a simple kind of guy.
Armadale inherits a large property in Norfolk, and invites Midwinter along to run the place with him. But Lydia Gwilt, the now-adult maid of one of the Armadale seniors thinks the property should go to her. She sets out a complex plan of marrying Midwinter (Who tells no-one his real name), dumping him, killing off Armadale and posing as Armadale's widow (Since the last name and first name would be the same on the wedding certificate). What could go wrong?
Gwilt takes up most of the rest of the book, and as driven and devoted as she is to getting her hands on the Armadale fortune, you gotta root for her. She's portrayed as a flame-haired goddess that no man can resist: Even a doctor called in an emergency to a dying man can't help but stare at her for a few minutes. And since this is Victorian England, a beautiful woman couldn't possibly conceive or carry out a crime, could they? Even when her backstory comes to light and it turns out that she was days away from hanging for a previous offence, her beauty lets her slip free.
Gwilt is a wonderfully realised villain (or even an anti-heroine) and a fully realised woman. Considering, again, this is Victorian England and a novel written by a man, Collins has nailed her mannerisms and determination and character. He gets into her head in a way that was forty or fifty years ahead of anyone else. But then, Collins always wrote such great female characters, far better than Dickens's two dimensional women.
As a for instance, you get to see Armadale from her point of view to hilarious effect, observing him as a love-stricken puppy who won't stop talking about his betrothed or his yacht. You practically cheer for her when she finally snaps at him after days of polite listening to his fatuous conversation. You feel for her when Midwinter's writing career locks him away for hours and hours, and she takes the distraction as lack of affection. Her absolute loneliness.
Most meaningfully, there's a chance for redemption for Gwilt when she marries Midwinter. She takes the opportunity to try and correct her life...because she really does love him, despite herself.
And it's that glimmer of humanity that keeps you rooting for her and keeps you turning the pages.