The game Breach takes place in 2123 after an experimental reactor using a new element called Excidiem caused a meltdown, transforming the planet. The player controls the defensive AI of the Excidiem core aboard an isolation sphere, defending it from enemy "Contagions" by moving along rails and using weapons. The goal is to protect the core as long as possible through increasing difficult levels until the unstable Excidiem explodes. Powerups and upgraded weapons can be earned to aid in defense.