Here are some rough ideas for the story;
A scientist is running experiments on some nocturnal animals and humans, trying to create humans that can see in the dark for military purposes. He is using some form of radiation and an accident happens causing his test subjects to mutate and become monstrous beasts, a humanoid nocturnal animal beast.
On a secret isolated island. A scientific research base is creating all kinds of weapons and the complexes main reactor starts to leak radiation which mutates the local wildlife, making one kind of dangerous animal species more savage and monstrous than before. These newly mutated creatures start attacking the base and killing the staff there. The only way to kill these monsters is to use the experimental weapons on the research base.