Duncan Mortimer was Sydney Sage's first ally in re-education. Duncan landed in re-education because he broke Alchemist rules to assist some Moroi while on an assignment. Duncan knows a lot about the workings of the Alchemist facility because he has been held for a long time. He comes across as having given up all hope at the chance of leaving the facility or escaping. We later discover that this is because he is the son of formidable Alchemist leaders Gordon and Sheila Mortimer.
Duncan knows that his parents won't allow him to leave re-education ever because pretending that their son doesn't exist is better than risking their reputation.
Duncan also treads very carefully in re-education and warns Sydney to do the same as, his friend Chantal was taken away by the Alchemists and he never saw her after that.