Team Scorpion must work with their old nemesis Mark Collins in order to prevent the extinction of mankind.

The team continue to work with their nemesis to prevent an extinction level event. Cabe makes a last minute decision that may endanger his career.

During the decommissioning of an old nuclear missile, the team is exposed to toxic vapor. Paige doesn't want Happy to tag along with her and Walter.

Team Scorpion is taken hostage during a tech convention.

A device that can prevent a nuclear meltdown is lost in the LA sewers and it is up to team Scorpion to find it while dealing with a new tenant next door.

The team goes to a renaissance festival but the revelry is short-lived when a group tries to rob a police evidence locker. Paige tires of Walter pointing out the anachronisms at the festival.

On Thanksgiving, Team Scorpion is tasked with destroying a floating island of plastic.

Team Scorpion tries to help a father and daughter involved in a plane crash. The team tries to help Cabe prepare for his trial. Paige helps Walter deal with his feelings about Cabe's possible prison future.

It's time for Cabe's trial and the team are anxious to know the outcome. They channel their nervous energy into saving a dog stuck in a cistern.

Walter takes a fall and is knocked out, his unconscious mind dreams of a world where Team Scorpion never existed.

Team Scorpion is locked in a doomsday bunker with artificial intelligence bent on killing them.

A solar storm knocks out power in Los Angeles, and Team Scorpion must help a teen pilot and his girlfriend who are lost over the Pacific without navigation or radio contact. Also, during the crisis, Walter must look after a group of Ralph's classmates, and Cabe tries to tell Allie finally that he loves her.

Team Scorpion must keep a tsunami from destroying a vulnerable nuclear plant. Toby helps his ex-fiancée recover her stolen identity.

When a helicopter crashes on top of a skyscraper on Valentine's Day, Team Scorpion must set aside their romantic plans and put them on hold to help save a doctor and pilot trapped inside the crashed chopper. Meanwhile, Happy and Toby await the news of their fertility test results and Sylvester realizes that he may have feelings for Florence.

After team Scorpion's mental faculties are impaired during a job to prevent the creation of a black hole, Paige must simplify the science for them. Florence and Sylvester grows closer after she helps him with a special project.

Team Scorpion is taken hostage after they inadvertently disrupt a bank heist.

The team must use their IQs to win a softball game when challenged by the director of homeland security to a game with all future contracts on the line.

Team Scorpion must save an unconscious, hypothermic boy stuck in the wheel well of their airborne plane; Paige realizes something's up when Walter's white lie takes a toll on him.

Team Scorpion heads to Northeast Africa where they must carefully navigate a minefield in order to save the lives of local villagers. Also, Paige and Walter's relationship takes a shocking turn, and Toby and Happy make an important decision.