Doctor Who: Rutans vs Sontarans: Grave Moon

The Doctor and Peri track a criminal imposter to a moon sanctuary of healing ponds, only to discover the lone Rutan the Doctor has previously met trapped in a self-made web of lies.
Experiments to rejoin the Host have forged a bond with grieving pond farmer, Ooland. As their mutual obsession tightens, so Ooland's ponds grow more polluted and their farm cut off from what is really happening on the moon: a full-on Rutan invasion.
As the Doctor and Peri strive to free Melmoth and Ooland from each other, another Doctor is at work close by - with far-reaching plans of his own for the lone Rutan.