Barry's friends fear his moving too fast in his relationship with Linda. Joe, having pulled Cisco into his new investigation of Nora Allen's murder, gets a call saying that the blood on the wall at Barry's house is Barry's own yet not kid's blood. Meanwhile, Dr. Wells and Caitlin find Ronnie under the possession of missing scientist Dr. Martin Stein. Tests reveal that, under stress from this duality, Ronnie's body will go nuclear unless he's put down or a way is found to safely split them apart in under two hours.