This is an unmissable achievement and is the first story-related achievement you will get.
At this point in the game (I found this after doing the first two secondary objectives), you will get a call on the radio from Prophet that there's something he wants you to see, that "you'll want to see this for yourself". Make your way to the objective marker; past a KPA checkpoint, go up the hill to the left and into a small clearing.
Prophet, Jester and Psycho are there, along with the Lusca's Call, which is a ship in the forest that has been completely frozen. During the cutscene, the achievement will pop, and shortly thereafter, Jester will be taken by one of the aliens and you will have to chase it.
WARNING. According to the comments, it is possible this achievement may not unlock as expected.