A toll of danger from deep within the TARDIS...
 
A deadly predator prowling the tunnels of London...
 
A high speed and high stakes race against time!

The Doctor is back in London, where an ancient beast is terrorising the city. As the Time Lord and her friends investigate, they uncover a mystery that will take them from a secret mountain base to the depths of the ocean - and, if they cannot solve it, one of them will perish!
 
Can the Doctor find a way through the maze of doom to save her friends?