Metamorphosis

The people of the planet Jaxus are vanishing. When the Doctor and his friends land, Naomi is snatched away by a mysterious fog and taken to a prison run by a very old foe of the Doctor's. The Master is here and he has, as ever, a sinister scheme underway... but neither Naomi nor Harry know who he is... Can the Doctor stop his plans and rescue the prisoners? Or will his companions inadvertently aid his enemy's plans?