When Team Scorpion travels to Ireland for Megan's one-year memorial, Walter discovers that a nearby lake's natural disaster has created a poisonous cloud that could kill everyone in the village. Also, Cabe and Toby try to alleviate the tension between Tim and Walter.

Walter must swim through the deadly La Brea Tar Pits when Team Scorpion helps a woman trapped in the tar before she runs out of oxygen. Also, without Paige's knowledge, her mother, Veronica, "helps" Ralph maximize his troop cookie sales.