Scorpion is tasked with helping Oksana Nastrova (Kathleen Munroe) of the Global Nuclear Energy Council move an improved concrete sarcophagus in place over the old deteriorating sarcophagus at the Chernobyl Nuclear Power Plant before corium trapped under the reactor destabilizes. Toby, who has diagnosed ex-Scorpion team member Mark Collins (Joshua Leonard) as insane, remains in Los Angeles for Collins’ competency hearing. Scorpion discovers unmelted caesium rods near the corium using a robot designed by Happy. While Paige and Sylvester fly with Oksana in her plane over the sarcophagus, taking measurements, the robot is affected by the radiation and punctures the corium, resulting in the ejection of a radioactive cloud that disables the plane. It crashes into the old dome, trapping the plane’s occupants while the team tries to save them and stop the corium from reaching the caesium rods. After returning to the United States, Walter tries to ask Paige out to a jazz festival, but decides to give her his tickets so that she can take Tim instead. Meanwhile, Toby covertly meets his jeweler in a parking garage to pick up a bespoke hex nut engagement ring for Happy, only to be kidnapped by Mark.