New halo at E3

sorry i might be all over the place in this thread but, bare with me and read! lol.

from watching the trailer of the new halo my mind began racing.

what is Chief doing in a desert?
was that giant bird a forerunner?
what of the Key that Halsey got during spartan ops?

my thoughts, the that the librarian gave Halsey could lead to cortana (with every key there is a door, and with every locked door there is something special behind it)
Chief’s new mission could be finding that door, to somehow save cortana, I’m pretty sure that all chief cares about right now is finding cortana, after all, what else would he need to do?

if you are wondering why i think the key leads to cortana, well, in other halos they made it clear that cortana is an extremely powerful weapon (destorys halo rings, kills didact, one of the covenants primary objectives is set to capturing her).

and from the looks of it, Chief could have abandoned or been abandoned by the UNSC. who knows, maybe he will somehow find the arbiter and they will join together to hunt for cortana, along with some marines like lasky who supported chief and cortana through the games.

what do you guys/girls think halos new story will be about?