Novelisation of the Doctor Who TV episodes/story of the same name.

Time itself is in peril! The three Doctors are united against an old enemy from the distant past of Gallifrey...

Vital cosmic energy is draining into a black hole and the Time Lords are under siege. The Doctor is their only hope but, trapped in the TARDIS, he's powerless. The only way out is to break the First Law of Time to let the Doctor help himself - literally...