Castiel is possessed by the leviathans and his vessel is about to explode. He goes to the Municipal Waters and the leviathans are released in the water. They possess a little girl, two swimmers from a high school team and a demolition worker and they are hungry. Meanwhile Sam confesses to Dean and Bobby that he has difficulties to identify what is real or hallucination and he sees Lucifer everywhere. The girl goes to the Sioux Falls General Hospital and possesses the surgeon Dr. Gaines. However Sheriff Jody Mills that is recovering from a surgery of appendices witnesses the leviathan eating the liver of her roommate and she calls Bobby. Meanwhile the four leviathans meet at the hospital and they eat the head nurse and one administrator. Bobby goes to the hospital and rescues Sheriff Mills. Meanwhile Sam is lured by Lucifer posing of Dean. When the real Dean comes to meet Sam, he needs to know how to find what is real.