Schapker appeared after Sydney was captured by the NSC and thrown into a secure prison inside Camp Williams. While there, she met a man named Campbell and became friends with him (despite his somewhat delirious mind). After talking for a while, Sydney felt sorry for him as the NSC had taken him away from his family and child - and he could only vaguely remember them.
With no other options, Robert Lindsey decided to force Sydney into revealing the coordinates by putting Campbell in harms way. He had a few of his agents stab him repeatedly and eventually Sydney told Lindsey everything... only to discover that Campbell never in danger; he was planted by Lindsey.
When Lauren came to the prison to find Sydney, she met Schapker right before the rescue operation led by Brill and Jack Bristow. Schapker knocked Reed to the ground and tried to stop their mission by shooting at the mercenaries. While Schapker was distracted and team was pinned down, Reed picked up a gun off the ground and used it to shoot Schapker in the chest.