Plot summary
When Walter's parents visit Megan as her condition worsens, the hospital is infected by a fatal fungus outbreak cutting Walter off from his sister and placing the whole team at risk. Thinking it is stachybotrys, the infectious disease unit searching for a cure collapse by spraying the wrong fungicide. It now falls to Scorpion to search for a cure themselves. Toby examines gold dust, a natural fungicide, on a cafeteria worker's boots and sees the man cut his leg, becoming a host to Meliola anfracta, an ancient fungus unearthed in soil.
In a surprising discovery, Sylvester's OCD about using antibacterials has caused him to grow a superbacteria on his hands that is fatal to the fungus. With help from Ralph and Cabe, who the CDC keep outside, they spread the bacteria through the water standpipes and save those trapped inside. Walter reaches Megan in time to be at her side as she dies. Later, he receives an email with a video from Megan telling him that, he is more than just his brain, he is his heart and he should not be afraid to love. As a result, Walter begins to open up to his estranged parents and holds hands with Paige while sharing memories of his beloved sister.
Credits
Adapted from Wikipedia contributors, List of Scorpion episodes. HTML formatting and reference markers removed.