Writer: Ronald D. Moore
Director: James Whitmore Jr.
Production Code: 2ADA13
First aired: February 5, 2001
Michael and Maria take refuge from Roswell together with Laurie. Max finds out hat a deadly parasite reached the ecological system of the earth, after the crash more then 50 years ago. Now, this alien parasite threatens to destroy the human race. With the attempt to destroy the parasite, Kyle and Alex walk into a deathtrap.
Shiri Appleby (Liz Parker), Jason Behr (Max Evans), Colin Hanks (Alex Whitman), Katherine Heigl (Isabel Evans), Majandra Delfino (Maria DeLuca), Brendan Fehr (Michael Guerin), Nick Wechsler (Kyle Valenti), Emilie de Ravin (Tess Harding), William Sadler (Sheriff Jim Valenti)
Jeremy Davidson (Grant Sorenson), Diane Farr (Amy DeLuca), Jason Peck (Deputy Hanson), Devon Gummersall (Sean DeLuca), Desmond Askew (Brody Davis), Allison Lange (Laurie DuPree), Heidi Swedberg (Meredith DuPree), Dennis Christopher (Bobby DuPree), Erica Gimpel (Agent Susan Duff), Rosana Potter (Carmen), Wendy Speake (Reporter)