Agent Hollister was the ranking Secret Service agent inside the presidential bunker during the events of Day 6.
Upon learning of the plot by Reed Pollock and Bruce Carson to assassinate President Wayne Palmer, Tom Lennox called Hollister and told him he needed to meet with him. Hollister informed Lennox that he couldn't leave his post, so Lennox would have to go him. However, before Lennox could get to Hollister, Reed assaulted Lennox with a flashlight and restrained him in the bunker's steam pipe trunk distribution venue. Pollock called to cancel the meeting between Hollister and Lennox, in order to divert suspicion away. The assassination plot was partially successful, as Palmer slipped into a comatose state. However, he was brought out and was stable for several hours, before he collapsed into it again.
Around 4:30am EST, it was discovered that a White House official leaked information to the Russian government. Tom Lennox discovered that Lisa Miller, Vice President Daniel's Chief Aide, unknowingly shared information with lobbyist Mark Bishop. In order to avoid charges of treason, Lisa agreed to go undercover and meet with Bishop. Hollister had surveillance equipment placed on Lisa, including audio and video. He waited with Tom outside of Lisa's apartment in a van. When Bishop was given an opportunity to upload data from Lisa's PDA, he took it, but he began to realize that something was wrong. He didn't go forward with the upload and he confronted Lisa on her mood. Hollister and Tom realized that things wouldn't go as planned and Lisa assaulted Bishop. He retaliated by strangling her and fortunately, Secret Service arrived in the apartment before she was killed. Lisa was rushed to the emergency room, while Tom set up negotiations with Bishop.