Noah Hicks was Sydney Bristow's ex-boyfriend. However, they wound up meeting each other again after Sydney was sent on a mission for SD-6.
Although Sydney re-welcomed Hicks and had a fling with him, several of the SD-6 employees (especially Dixon) believed he was a traitor.
After Noah and Sydney went on an infiltration mission together (which almost failed when Sydney nearly set off the alarms) they met each other on a beach and Noah seemed to convince Sydney to give him a week with him on an island in the South Pacific to see that they could start a new life together. Sydney agreed to the week and took the plane ticket he had for her. Noah called to talk to Sydney from his plane but she told him that she couldn't go with him (i.e. because of her search for her mother). He says he understands and they say goodbye.
When Sydney was sent to a mission in Australia to find a VIP under the alias of Calder, she realized that both Calder and all of his guards had been murdered by an assassin. Sydney fought the assassin briefly, the assassin rolling onto a knife used in the fight after he hesitates to kill her. As Sydney took off the assailant's mask, she suddenly found out that it was Noah; he was a double agent for K-Directorate. Noah said a hoarse goodbye to Sydney as she watched him die with tears in her eyes.