One Shot:The Wizard on the Moor

A village has a central source of vitality and power that's been fueling the people there for decades. It was a gift long ago from a strange little man who asked for shelter here and was treated with kindness, even in a time of scarcity. (The story lives large among the townsfolk still, as well as those in the immediate larger region.)
A nearby moor is a sore-spot among the villagers; it seems a breeding group for wicked things, and more than just mosquitoes. What to do with that land, they didn't know, and meanwhile they felt its danger encroaching more and more each year.
One day a dashing old wizard found his way to the town and charmed the people with his disarming ways and neat magic tricks.
When he offered to buy the moor, they were overjoyed to let it go. After all, they could use the gold to buy healthy livestock and to rejuvinate their merchants' row. They sold the moorland and threw a party for their new neighbor.
The Wizard, it turns out, knew more about the well-water than did the townsfolk. He understood that it was magically designed to tap the energy of the very earth below, and bring it to the surface.
This enchantment thus encompassed a great swath of groundwater emanating from the place of the well. He knew also that the waters of the moor mingled with those magic waters. And he wanted his own access to that magical power.
So he set to constructing conduits from the enchanted groundwater, "setting up shop," purely distilled to his own dwelling, where he basked and basked, as if from the effects of some drug.
Meanwhile the people of the town found their well-water.... different somehow. The energy they'd felt for these decades slowly ebbed, and depression settled in. Plants wilted and livestock got sicker, neighbors no longer wanted to greet each other in the streets.
The Wizard didn't stop at this. He hired to hench-goblins to return to the town and steal back his gold. The more he himself fed on the enchanted life-force, the more bold and diabolical he became, the more power hungry and manic.
Who will help with this?  Heroes that gathered in the town incidentally, or those who were passing through for whatever reason, must agree to help.  To assist (if necessary), the original enchanters of the well may come by and offer a boon or magic of some kind to those who wish to help defeat the wizard.