To fix a Los Angeles nuclear reactor that's on the verge of a cataclysmic meltdown, Walter and the team must reluctantly enlist the help of a troubled former member.

Team Scorpion must outthink their unstable ex-Scorpion member, Mark Collins, after he kidnaps Toby and threatens to kill him unless his cunning demands are met.

Team Scorpion must find a boy from Ralph’s class who goes missing on a field trip after he accidentally has a run-in with a deadly criminal. Also, Toby gets closer to finding out the identity of Happy’s husband.

Team Scorpion must work with their old nemesis Mark Collins in order to prevent the extinction of mankind. Also, Walter and Paige awkwardly navigate their new relationship.

Team Scorpion continues to work with their nemesis, Mark Collins, in order to prevent an extinction event that could end humanity. Also, Cabe’s last-minute decision while on the case leads to the possible end of his career.