The final installment in the Engelsfors trilogy finds the remaining members of The Circle trying to save the world from demonic forces while also dealing with their normal high school issues as they head toward graduation. Meanwhile the Chosen Ones who died over the last two novels are stuck in the Borderland desperate to help. The world-building by the authors has been fantastic over the course of the trilogy, but by the time The Key was reached, the story had been excruciatingly stretched out. With much of the first half of The Key spent rehashing plot points from the first two books, the action of The Key comes far too late.
Review copy provided by the publisher, Overlook.