A parasitic worm turns Pete and Chloe into daredevils, and Clark joins them on a dangerous adventure.
Lana decides to enroll at Metropolis University at the last minute and is forced to join the Tri Psi Sorority, a sisterhood of vampires. Clark discovers Lana has turned into a vampire when she attacks Chloe at a Halloween party.
Callen must infiltrate a network of Chechen terrorists who are recruiting fighters to join their cause as they plan their next attack on the U.S.
As Ilaria CEO Constance Sutton arrives to collect the virus and its cure, Alan finds Walker (Kyra Zagorsky) seemingly symptom-free. Daniel (Meegwun Fairbrother) learns the truth about his “adoption” by Hatake (Hiroyuki Sanada).
In a last ditch effort to find help and a cure, Alan and Julia go to an abandoned satellite station discover a shocking secret that reveals Hatake's ultimate goal and the reason why he has developed the deadly virus.