The cat had lived a long, hard life and wanted to return to the house. The house it was born in to. The house it had been chased from as a pest. The house, that, finally, had been abandoned by the humans.
On its return, it found the house was infested with mice. The mice were everywhere, in the kitchen, the bedrooms, the living rooms, the library, the hallways. Everywhere. The cat set about removing the mice from as many of the rooms as it could manage. Until the mice were restricted to the basement.
Content the cat slept.
But the mice were too many to live in that one small space.
Some mice tried to scavage for food, but when they did the cat ate them.
Some tried to escape, but when they did the cat ate them.
Some tried to fight the cat, but when they did the cat ate them.
So the mice came up with a plan. They would drive the cat away.
They scritched and scratched inside the walls as the cat tried to sleep.
They moved things when the cat wasn't looking.
They polluted his food and water with their droppings.
They didn't drive the cat away, they drove the cat mad.
The mad cat, instead of slinking off to sleep elsewhere, instead of finding somewhere where things stayed where they where put, instead of finding food and water elsewhere, the mad cat only saw mice everywhere and seeing them wanted them dead.
Every last mouse became the enemy of the cat they drove mad.
Every last mouse became a blur of blood and skin and fur as the cat rendered it down to a smear.
The cat didn't discriminate between the mice. Mouse, pup, buck or doe, none were spared his murderous rage.
Eventually, all the mice were gone.
But the scratching and scritching, the cat was sure it could hear it.
And the things never seemed to be where the cat left them.
And the food and water tasted... wrong...
And now the birds.
The birds outside.
They looked like they were planning something.