The series takes place in a world similar to our own but one where vampires, witches, werewolves and shape-shifters live among humans without their knowledge. These supernatural races make up a secret society known as the Night World, which enforces two fundamental laws to prevent discovery: 1) Never allow humans to gain knowledge of the Night World's existence and, 2) Never fall in love with one of them.
In Spellbinder the plot centers on Thea and Blaise Harman, cousins who belong to the race of witches. Although they are as close as sisters, in temperament the girls are as different as day from night; Thea belongs to Circle Twilight, for the not-so-wicked-witches and Blaise belongs to Circle Midnight, for the darker ones. When the two cousins start fighting over Eric Ross there ensures an epic battle between black and white magic.