4. Code Yellow

Deke Shaw is revealed to have started a company using S.H.I.E.L.D.'s tech. Sarge and his team track down a seemingly normal man and kill him with a strange knife. The body is brought to Benson, who discovers a bat-like alien parasite that revives and flies into the vent system after the knife is removed. Sarge's team goes after Shaw as their next target, with Sarge pretending to be Coulson to get close to Shaw. Eventually, Deke realizes it is not Coulson and attempts to escape, aided by an undercover S.H.I.E.L.D. agent assigned to keep an eye on him.

Mack, May, and a strike team enter the building and attempt to apprehend Sarge and his group alive. Though Mack is able to capture Pax and Jaco while May defeats Snowflake, Sarge gets the upper hand and kidnaps May. While tracking the parasite, it flies into Agent Keller 's mouth and starts fusing with his vascular system. Benson and Yo-Yo attempt to get him to a containment room, but he explodes in a mass of crystalline structures. Yo-Yo retrieves the knife and stops the parasite from destroying the base, but is left devastated by her failure to save Keller.