The Circle Series, formerly known as the Circle Trilogy until the novel Green was released in September 2009, is a set of spiritually inspired novels by Ted Dekker, written mostly in 2004, about a man named Thomas Hunter who, after a head injury, wakes up in an alternate reality every time he goes to sleep. The stakes are raised when he realizes that a deadly virus is about to be unleashed on our world, and that the other earth is also being threatened with catastrophe. The pace quickens as links and parallels between the two worlds are revealed, and the clock begins to run down for both worlds.
The Circle Series takes place in the same universe as several other Dekker novels, and makes several references to them. These other novels include the Paradise Novels, the Lost Books, Skin, House, and Immanuel's Veins.
Originally, Green was called "The Beginning and the End," and was meant to be both the first and the last book of the series, causing an infinite loop in the timeline. Many fans were confused and spoke out about this, so Dekker wrote a new ending to Green called "The Last Stand" which brought a level of closure to the series. It can be found in the 4-in-1 collector's edition, The Circle.