Evil sorcerer takes over a small domain, some small hamlets and farms
Hero goes to go fight him, takes shelter for a night in a cowbarn
Sorcerer activates spell remotely, "I don't need adventurers, I do need some workers. Or more cattle. Huh. Why not both?"
Hero's equipment is pulled off and tossed around
Hero left naked, magical energies tingling
Half-grown cow walks up, hero is placed laying atop of its back
"Yes, both. Both is good."
Hero's feels a weird sensation as his feet and hands sink into the cow
Cow's hooves start to reshape to hands, hero feels them
The hero continues to sink into the cow, who shifts and grows into a more humanoid form, there masses combining
Hero's hips fully merge, the cow's cracking and reshaping, the new sensation of an udder pulling at him
Hero continues to sink and merge until only his head is left, sinks into the cow's, which reshapes to become more humanoid
Vision goes dark, then he opens his eyes, his body fully merged with the cow's
Her body, as she stands up to take stock
"Like this will stop me, you sorcere-" magical energies hold her mouth shut
"Oh, you're not quite done yet."
One by one, the adventurer's equipment is transformed into a tool a peasant farmer would use, memories and experience using them fading 
Along with each item, her body becomes more sturdy and fertile; breasts and udders well, muscles toughen from rough labor
Journal is last, burning page by page as the ability to read fades, the cover and binding changing to become a collar and bell that wrap around her neck
the bell rings, and her eyes become dull. The bell rings several times, and her anger and fear are replaced with a glowing softly pleasurable sense of placid contentment
Notices that her udder is full and needs milking, begins to do so, each squirt of milk causing her memories to fade further and further, replaced by vauge memories of working on the farm.
She finishes up milking, then puts on her clothing to properly store it and get back to work on the farm.