Between Worlds is the 20th book of the Charmed novels.
The novel takes place from October 30—November 1, thus placing it between Season 4 Episode 6 A Knight to Remember and Episode 12 Lost and Bound. This places it ahead of several other novels chronologically even though it was published several months later.
Recent melting of buildings prompts the discovery that something is attempting to destroy the 'wards' between the worlds of the living and the dead by using the untrained witch Claire Katherine 'C. K.' Piers as its agent through the De Vermis Mysteriis (Mysteries of the Worm) book, supposedly created by a powerful male witch who then used it to contain his evil brother 500 years ago.
- C.K. Piers: A witch.
- The book never specifies whether or not Cole is still Belthazor at this point, as he is never in a position where he would have to use his powers if he possessed them. Although he did speak about the possibility of becoming a demon again, when C.K. said 'You all have powers?', she wasn't corrected.
- Paige implies that she has already received the power to heal; however, she does not actually activate this power until later seasons.
Russian: Mježdu mirami (Between worlds)