One day mysterious Gateways began appearing on Earth, randomly popping up in different places at different times. They appear to be openings that lead to alternate worlds and alien dimensions. From these Gateways, various Entities would emerge into our world, some little more than alien animals, others defying logic or explanation, some driven purely by instinct and others having intelligence rivaling that of humans.

To combat the threat, a secret government Organization was formed with the purpose of studying and containing the mysterious Entities and Gateways, neutralizing them if necessary. Naturally, other organizations would also form, with their goals or methods of going about, from destroying Entities on sight regardless of the threat they pose to finding ways to exploit them for their own gain.