This isn't my thread. This was copied from the Halo 4 forums on Waypoint. I want to know what the users here think about it, because it seems a bit outlandish.
Ok so after reading Glasslands and Primordium, I believe I know what will be the backstory to Halo 4.
In Primordium it says that the UNSC has ONI scientists stationed at the Ark. This means that ONI must have reopened the portal on Earth. The flood on the Ark was destroyed during Installation-04B's premature explosion (lol.) While damaged, the Ark still supports gravity. ONI scientists have found the terminals that John found and learned of the Librarian, the Didact, and anything else the terminals talk about. While there they find a duplicate of 343 Guilty Spark. This duplicate was made of himself while he was on the Ark (either during Halo 3 or during the Flood-Forerunner war.)
When the Portal closed at the end of H3, it just sent the Forward Unto Dawn several lightyears away from the Ark. Once Cortana's beacon was activated, it took over 5 years or more to get to the scientists stationed on the Ark. This lets them know that Master Chief is still alive. They contact Earth via the Portal, Earth sends the UNSC Infinity that contains a Mark VII suit. The ship goes through the Portal to the Ark. With the Forerunner slipspace drive on the Infinity, the captain jumps to the signals location, which takes possibly a couple weeks or days.
Here's a few possibilities on how the Infinity finds John at the Shield World. They mind find the ship exploding from the strain of the Shield World's tractor beam. They manage to get John out and treat his injuries and such on the Infinity, and fit him with the Mark VII. Then the ONI agents on the ship send units into the Shield World, knowing that Forerunner technology could be useful.
Or they arrive and John is already in the Shield World and send in troops to recover him, and give him the Mark VII once they find him.
Spartan-IVs are on the Infinity so we'll definitely see them. Also it's most likely that we'll see Fred, Kelly and Linda. During a 4-player Co-Op, players will paly as these 4 main Spartan-IIs. The host is obviously John with everybody else being Fred, Kelly and Linda. Naomi may or may not make an appearance.
Also the Mark VII has very unique abilities such as transforming the energy shield for multiple purposes, such as energy daggers and walls. Possible new gameplay elements or armor abilities?