Well, this is one of those stories where you start with a simple topic. For example: IF there's a fire, this happens. If that happens, this happens. If that happens, then this happens. IF this happens, the fish dies. IT can be as long as you want it to be, it just has to start out with if there's a fire, and you have to end with The fish dies.
If there's a fire, everybody leaves.
If everybody leaves, the fish starts to panick.
If the fish starts to panick, it runs into the side of the bowl.
If it runs into the side of the bowl, it will get a concussion.
If it gets a concussion, it will go to the vet.
If it goes to the vet, it meets a cat.
If it meets a cat, the cat eats it.
If the cat eats it, the vet takes the cat into surgerey.
If the cat goes into surgerey, they find the fish.
If they find the fish, they will try to save it.
If they try to save it, the fish lives.
If the fish lives, they will keep it as a pet.
If they keep it as a pet, they forget to clean it.
If they forget to clean it, the bowl gets dirty.
If the bowl gets dirty, the fish eats the poisonous algae growing on the sides of its bowl.
If the fish eats the poisonous algae growing in the sides of its bowl, the fish dies.