Full Metal Panic! Surplus summary:

When an unknown Arm Slave surfaces somewhere in the Taiwan Strait near mainland China, MITHRIL orders Melissa Mao and her team to go into a divided Hong Kong to investigate the perpetrator of the unknown Arm Slave. As the team continues to check into the reports of the unknown Arm Slave, the culprit is believed to be a potential SRT recruit back from Sousuke's training days in Belize when he was not recruited by MITHRIL.