This requires "The Slingshot Content Pack". If Zhang has been part of anything completed, this achievement will be available. This is a Unique Council mission that is part of the DLC, and can be done under any difficulty setting. When selecting a squad, consider that the follow-up mission aboard the alien battleship will start after Confounding Light's completion and not allow time for wounded soldiers to recover. The mission has a ten turn time limit. Activating transponders will not extend the time limit. Your squad must advance quickly enough to place all four transponders and reach the train's control console within that time limit. Reaching the control console with your last action in the last turn will still be a failure. Eliminating all opposition is not required to complete the mission. Aliens who are not an immediate threat should usually be ignored to focus on the transponders. Only one soldier needs to reach the train's controls. A Sniper with Damn Good Ground and Low Profile can hang back and take advantage of high ground and low cover by climbing the ladder at the rear of the train, then advancing slowly along the roof. An Assault with Lightning Reflexes can be used to counter the aliens' frequent Overwatch use. If possible, consider replacing a Sniper or Heavy with a second Assault, as Run & Gun may also be useful. A Support with the Sprinter ability may be also do well. Keep a Heavy with a rocket in reserve to clear the control room quickly; a pair of Thin Men occasionally will be holed up inside. Damaging the train during the mission is allowable.