This is the 60th novel published by the BBC to feature the 8th Doctor.  His companions are Fitz Kreiner and Anji Kapoor.

The Doctor has dropped off Fitz in the 1800's to journey to Siberia.  He has also dropped Anji off in 21st century London, three weeks after she originally left, to continue her life.

Fitz meets up with dangerous dinosaur like creatures from an alternate reality that have passed into the 'real' world.  Anji gets taken by a group of Americans to capture a time machine that does not exist.  The Doctor just happens to be going there too.

Fitz dies (or maybe he doesn't) and there are two possibilities created in the same universe.  Before Fitz dies, he uses a grenade near a black hole to release an incredible amount of energy that causes the 'split.'  The Doctor and Anji work together with some of the visitors to stop the American commando team, on orders from Control,  from killing everyone.

Fitz is liberated from the 'possibility' trap and everything is put to rights.  Sabbath's hand is revealed in the paradox.  He leaves on the Jonah, but not before the Doctor, Anji and Fitz see them.

When the Doctor stops off to see that a certain event that happened in the past will happen again, they discover that they have entered into an alternate universe and that they must not return Anji to London.  They must put wrong to right again…

A man stands.  Frozen in time.  The chill breeze from the open door ripples the cracked pages of the book he holds.
    The Doctor hesitates.  Should he buy the book anyway?  A curiosity?  A coincidence?  Or a distraction.  He has more than enough to do.
  With a sudden dust-clouding movement that makes the old woman blink and shiver, he snaps the book shut.  He refolds his piece of paper, a quick well-practised routine.
    And he reaches out to replace the book on the shelf.
    The book slides easily into its dusty place.  But the Doctor hesitates, the book half-in and half-out.  A decision, a turning point.  If he leaves it now, he will never know for sure.  And what does he have to lose?
    He pulls the book out again, and turns to smile at the old woman counting the money.