Doctor Who and the Serpent's Mask

"Doctor, you are under suspicion of the Stolen Ancient Text in Samaritan History"

The Doctor and his friends been traveled to another world, a Utopian World but the Doctor knows that every of these so calls perfect world has a Serpent, as one has stolen an Ancient Text and is now drain power from individual Samaritans one-by-one slowly and surely. It's up to the TARDIS Team to solve and put to the end of this Crisis