Two minuscule quibbles:
"More than two years earlier – twenty-eight months ago, to be exact -- he received a call from someone claiming that the Secretary of the State wished to talk to him." should be Secretary of State, not the state.
"When they arrived, he saw several armed soldiers guarding the entrance to elevator to the scaffolding. After checking his credentials, he entered the elevator." consider he was allowed to enter the elevator. That subtly emphasizes that he could be barred (or shot) should he fail inspection and try to enter anyway.
You've established tension in the first paragraph, and Sarah is mostly isolated and Jason is still in play.
You've set the stage with the team, will one of them be a plant, unhinged or a traitor to the species?
It wouldn't be difficult for the aliens to be more likable than our fellow humans. Or present themselves as such!
Oh, that is in the works. Turns out there are over 7000 alien races with this level of advanced technology in our galaxy. There is a large communication network, that we will be admitted to ... once we learn how to communicate.
____________________________________________________________________ I would say “After presenting his credentials, he was allowed to enter the elevator…”