Welcome to the Revolution

Welcome to the Revolution is the prologue of Deus Ex: Human Revolution.

Sarif Industries laboratory
You start at Megan Reed's office. There's some "point and click" to do. The important ones that are required to get the Old School Gamer achievement are:

After you leave the office, you will automatically follow Megan through a couple of labs, and be introduced with the plot. At one point a cutscene will play, showing Adam and Megan going into the elevator. Frank Pritchard will join them shortly after, and have an argument with Adam after Megan leaves the elevator.
 * Toy car
 * Book Being More Effective
 * Portrait of Megan and Darrow
 * Megan's computer
 * Picus newspaper
 * Ebook containing Megan's notes on Patient X

Speak to David Sarif
Afterwards, you'll arrive at Sarif's penthouse, and enter his office. After few more moments of chatting, an alarm will sound. You will be sent via Sarif's personal elevator to check what is happening. The elevator code is 0451.

Pritchard will tell you the approximate location of Dr. Reed, and that there's interference with the comm signal coming from somewhere. After that, the contact will be lost, and you'll exit the elevator on another floor of laboratories.

Investigating the disturbance
It's a pretty linear path, simply move through the corridors and open doors. At one point, you'll witness Lawrence Barrett killing two scientists. Turn to the left and remove crates by a vent, which you'll use to continue on. The first enemies you'll encounter will be in an empty lab with stairs leading up to the 2nd floor. Just take cover and aim for the head. Since the Combat rifle in the prologue is fully upgraded, they won't pose too much of a challenge.

Move up the stairs through the doors, and continue on to another small lab. Best tactic here is to take cover by the door, open it, take out the two enemies standing ahead, then finish off the last one in similar fashion. Once you've dealt with them, go out the opposite door.

A little later, you'll see Yelena Fedorova gun down three security guards, and a scientist afterwards. Move through the doors he managed to open with his dying breath, and take cover. Four enemies will come through the door below. Again, stay in cover and aim carefully, and you'll be fine. Cover and shoot-and-hide tactic is your best friend here.

Exit the lab and continue through the corridor. The end level cutscene will follow.

Video Walkthrough
This video shows you the integral parts of this mission, as well as how to get past the guards without killing anyone (pacifist approved!)