All the way back to the 1960s and the villains Silver Age origins. Spider-Man and Green Goblin go back a long way. At this point in the game though, you likely have the means to clear out the palace and get back the prisoner with relative ease. If for some reason you arrive too late and the prisoner has been transported, the mission does not change, however you will have a much bigger fight on your hands to get him back. Once you have the prisoner extracted, the mission is over so you can exit the area through your helicopter. If the Walker Gears are there, you can simply destroy them, or tranq/kill the pilots then Fulton out the prisoner. To make things easy, we recommend moving to him quickly, before he gets transported. If you take several minutes, he may simply be gone as the soldiers have decided to move him, in which case you need to extract him from the more heavily defended area. Depending on the time frame it took for you to arrive, you will see him under a few conditions, either he is alone and can be extracted, or he is surrounded by Walker Gears.
Shortly after getting past the outpost you will spot your objective.