Cheung was a deep cover CIA agent who worked on Project Red Bell alongside Robert Hawkins, Sarah Mason, Victor Miller, and Chavez under Thomas Valente. Some time after the September Attacks when Chavez and Hawkins reunited, Chavez confided in Hawkins that the two of them and Cheung were the only members of their team to still be alive. After the attacks, Cheung remained loyal to the US federal government and went undercover as a Jennings & Rall employee in the headquarters to continue investigating the Cheyenne government.
When Hawkins and Jake Green reached Cheyenne following the decision to bring the final remaining nuclear device from the attacks to the Independent Republic of Texas embassy to conclusively prove the Cheyenne government was behind the attacks, Hawkins contacted him through a coded fax message. While Cheung did meet with them, he refused to trust Green. As the trio prepared to move the bomb to the Texas embassy, John Smith, the man behind the attacks, attacked them, shooting and killing Cheung and wounding Hawkins.