The Power of Two (Book One)

As a Charmed One, Phoebe Halliwell is used to the out of the ordinary. Her older sister, Prue, just survived a potentially deadly attack by the demon, Shax, and her past boyfriend, Cole Turner, was a servant for the Source of All Evil.
But she never expected that she would get to travel through time and space with a man called the Doctor, the last of the Time Lords. During her travels, Phoebe witnesses the day Earth died in a big ball of fire, learns the outcome of messing up fixed points in time when she tries to save her mother from her watery grave, and faces the consequences when she takes pity on the last Dalek in the Universe. And two words seem to be following the Time Lord and the Charmed One everywhere they go: Bad Wolf.

Cover by @Chell-P