There are spoilers for Control as well as the trailer for Control Resonant. Read at your own risk if you haven't played the game.<< Replaying Control, part 3: Directorial OverrideOld Boys' Club
The Sector Elevator now leads to the Research Sector. Jesse steps out into Central Research and is greeted by a video of Dr. Darling welcoming visitors from other parts of the Oldest House.
This is one of the areas of the game where ray tracing makes a huge difference. There are a massive number of reflective surfaces in Central Research, which actually made reading some signs (and the map) a little difficult.

As pretty and impressive as it is, I feel like the ray tracing gets a little too distracting sometimes. The text on this map is barely readable at certain angles.
After fighting off some Hiss and destroying some Hiss clusters (red cube-like things that block off areas), Jesse can now proceed to Parapsychology to find Marshall. But before that, I did some exploring in Central Research. There are plenty of documents to find, another video by Dr. Darling, and at the very bottom of Central Research, an acoustic room where you can listen to
My Dark Disquiet by Poets of the Fall. The lyrics are on a chalkboard right outside.

Poets of the Fall are the real-life band that perform all of Old Gods of Asgard's songs in the Remedyverse. This particular song isn't an Old Gods song, but we will hear an Old Gods song later in the game.
Though, that does raise the question: if the Old Gods didn't perform this song in-universe, then who did?
After going through the doors to Parapsychology, we get a message from Marshall, who's in trouble. The straightforward path to Marshall is blocked by the Hiss, so Jesse has to take a different route through the Sector. As you may have guessed, there are plenty of Hiss in the way.
This route takes Jesse through the Astral Exhibition, which contains multiple videos by Dr. Darling explaining the Astral Plane, a diorama of part of the Astral Plane, and behind that diorama, a video projection of…something, presumably in the Astral Plane.

One of those Darling videos explains that an Astral Spike came back from the Astral Plane with an FBC agent, and now they keep it in the Astral Exhibition. Except with the Hiss and the lockdown, it's gotten out of containment and Jesse needs to put it back in.
Astral Spikes can't be harmed, so Jesse has to lure it in and wait until it's in the right place before closing doors quickly enough that it can't follow her. This can be difficult to time properly if you aren't properly making use of Evade.
Outside of the Astral Exhibition is a loudspeaker that Jesse tries to use to communicate (unsuccessfully) with Marshall. After going through Parapsychology, fighting off some Hiss, and cleansing a Control Point, the area returns to relatively normal, and Jesse can use an intercom near the elevators to finally, properly talk to Marshall.
It's a very brief conversation where Marshall says she'll send the elevator, and then more Hiss appear. Even Jesse is annoyed by this. The elevator (if you look closely, it says PAINE ELEVATORS) takes Jesse to a part of Central Research that can't be reached without Levitate. One you get that power, there is no reason to use the elevator anymore.
Marshall and her people are currently holed up in Luck and Probability. Marshall isn't at all surprised to see Jesse, or that Trench is dead, or that Jesse is now the Director. She gets right to the point: they need to make more HRAs, but the lab isn't secure and they need Jesse's help.
Jesse's sent in to the Ritual Division, where there are rangers fighting off Hiss. It's a very red area and remains red until all the Hiss are defeated and Jesse cleanses the control point. Keeping the rangers alive tends to be pretty difficult – not just here, but in other parts of the game where rangers show up – and I think I've ended this fight with one alive at most. That’s because there are two phases to this fight. The first phase has Jesse fighting regular Hiss, and the second has a named Hiss (a miniboss) with some regular Hiss.
Jesse can now proceed to Protective Studies. There is a rubber duck Altered Item stored here. Remember the duck. It doesn't have any plot significance whatsoever, but it does show up later.

The HRA Lab is past a hallway. Jesse needs to solve a very simple puzzle to get in (the answer is right there) and then activate the HRA machine. Naturally, the machine isn't working and Jesse needs to fix that by completing another puzzle: putting the correct punch cards in the correct terminals. The symbols on the whiteboards, as well as the notes in red marker, show the correct sequence.
Marshall and her people arrive at this point. Marshall also does this thing that's common in modern video games where she comments on what the player needs to do to solve the puzzle without actually giving the player any time to figure things out. Bit annoying, really.
Jesse turns on the HRA machine and it destroys the Black Rock prism sample they have. Now they need more; Darling's got another lab in the Maintenance Sector where he keeps the prisms.
Before Jesse heads off to Maintenance, she asks Marshall about Dylan. Marshall won't give Jesse any answers until the HRA machine is fixed, which Jesse reluctantly admits is the right thing to do. Once Jesse has a new Black Rock prism, she'll meet up with Marshall in Central Executive.
When the mission ends, we're treated to a vision – perhaps – of Trench watching a video of Darling, where he seems to have predicted the Hiss invasion, and created the HRAs to counter it.
After that, Marshall opens up a door that leads directly back to Central Research. No more taking the long away around now!