In 1975, Callahan began working as secretary for the OSI, replacing Miss Johnson after her three month extension expired. (Steve Austin, Fugitive) Her original OSI security clearance was Level 3. However, when a gunshot wound damaged the power cable and circuitry in Steve Austin's bionic leg, she was asked to gather electronic components to assist repairs when Dr. Rudy Wells was unavailable. As a result of this top secret information being revealed, Callahan's OSI security clearance was upgraded to Level 6.