: Just seems odd that Spirit of Fire would be all alone there. there would have
: to be some kind of UNSC presence.

: Sorry, I have not kept up with any of the books/comics since the 2nd
: forerunner book.

The beginning cinematics and mission to HW2 have already been released as promotional/preview material. If you're fine knowing what happens before playing, they addressed the above.

There are several research installations on the Ark, and Isabel was a logistics AI at one. But the Portal to Earth shut down when Cortana took over the Created, and soon after the Banished arrived and laid waste to everything. When you get to the Luther Mann research outpost (nice touch to Halo: Hunters In the Dark) everybody is dead.

We don't know if anyone survived and plays into the game's plot later.