The Indigo Spell picks up very shortly after the end of The Golden Lily. Sydney is given a mysterious assignment that involves using her magical powers, something we all know she looooves. She's given the barest amount of information, but with some prodding, Sydney learns that she's in a bit of a catch-22. Taking on this assignment could be very dangerous. However, NOT acting could prove much worse (this is a spoiler-y part, albeit a very early one, so I won't go any deeper. Suffice to say, it is downright sinister.)
Because Sydney is not content with just one potentially deadly mission, she decides to multitask and seek out former alchemist, Marcus Finch. She believes he can tell her secrets of the Alchemists and how to escape the bind that keeps her trapped in their service for life. As we know, Sydney's developing relationships with vampires, the monsters whom she is supposed to hate, make her question the beliefs of the majority of her kind.
When I first heard Richelle Mead was going to spin off Sydney, I thought, "Huh, why? She's so BORING!" But I've grown to really like Sydney, and even more so in The Indigo Spell. She is a living, breathing human now, not just a machine.
And Adrian...ah, Adrian. Now that he has professed his feelings for Sydney, he seems to pop up everywhere. Sydney professes annoyance, but we all know better. Adrian has grown so much, and he is now easy to view as a believable, desirable love prospect, and just perfect for Sydney. I know she knows it, too; she just needs her walls broken down, and Adrian is more than willing to try and try some more. There's a forbidden Romeo and Juliet quality to their relationship that makes it even more compelling.
The story, which I have avoided discussing, is exciting and intense. Mead has a great talent for writing these kinds of scenes. Mead also loves to throw in a last-minute twist regarding her villain(s). Typically, I can see it coming from a mile away, but I'm pleased to say this one took me by surprise.
I loved Sydney's final scene with Adrian, and the last couple of pages feature a surprise visitor to Sydney's room that left me smiling because it promises some awkward (in a good way, I hope) complications for Sydney in the sequel.
I would recommend reading the full Bloodlines series before picking up The Indigo Spell. But if you insist, an early wedding scene gives a brief introduction to important characters and their backgrounds.