Along with two fellow Security men, Barnes and Lieutenant Emigh, Padilla accompanied Admiral James T. Kirk, Commander Spock and Dr. Leonard McCoy on a visit to the colony planet Calibus VII. The colony was ravaged by a zombie virus, which infected Padilla when an apparently dead colonist scratched him on the hand. Padilla transformed into a zombie and bit Barnes when he attempted to see what was wrong, infecting him as well. Emigh also became infected.
McCoy subsequently developed a serum to control the zombie virus. Padilla, Barnes and Emigh were restored to sanity, but their bodies remained ravaged and gray-skinned from the virus, which was dormant in their systems, not fully eliminated. The three Security men were forced to remain on the planet, which was quarantined under General Order 7, but McCoy promised them that he would continue working toward a cure. (TOS comic: "Infestation")