The Colour of Darkness

The Tenth Doctor is in pursuit of the robot Agent and the Eternity Crystal. His travels have taken him to the forbidding planet of the Darksmith Collective, Karagula. Before the Doctor can reach the hidden Dark Cathedral, he arrives at a village without any children. It is a mystery that the Doctor must unlock before he can find the Crystal. Will the Doctor solve the mystery and will he find the Crystal before the Darksmiths retrieve it?