You begin the first act in the TEGEL Airport, where agent Maria Lovelette informs you that a copter was shot down in an effort to frame you, and that a man called Condor knows where a vaccine is. Condor is currently in hiding somewhere in East Berlin, and she asks you to take out the group trying to kill him.
After you agree to take the case, you start out on the west side of a long street in East Berlin. You have full health and no bullets, so your only means of attacking is to kick enemies until you defeat one and obtain ammunition. The first enemy agent will attack you when you reach Potsdam Station, which is currently empty. The next man you encounter is not an agent, but rather an informant.
Another enemy agent will attack you before the first ambush occurs. Upon being ambushed, you switch to first person perspective, and you must defeat four enemy agents in gun combat before you can move from your location. When you return to the side-scrolling portion of the game, a motorcyclist will pass by in an attempt to attack you. Another enemy agent will attack just outside of Friedrich Street Station. Inside the station, you'll meet Dirk Bullit. He tells you that someone in your agency has a helicopter. Exit the station and make your way to the next section of East Berlin.
More agents will attack as you approach the Alexander Hotel. If you enter it at this time, you will be told that no rooms are available. Continue fighting a few more enemy agents until the next ambush occurs. This time, you will face three agents and two helicopters. Take out the three agents on the ground first as they are easier to find and deal with. Then find one helicopter and destroy it. When you are down to one more helicopter, the game will indicate whether you can find it to the right or left. You'll encounter many more agents on your way to Alexander Station. Inside, Cherry Grace will introduce herself. She informs you than an enemy sniper is in a television tower waiting to kill Condor and that a helicopter is waiting nearby. She also asks you to visit the hotel when you're done.
After meeting Cherry, you immediately embark on the helicopter. In order to get to your destination, you will have to fly through a section of enemy air space. You will be attacked by jets and bombers along the way. Attack the jets if you can, but stay out of their way. When bombers appear, let them get ahead of you, and then get behind them and fire at them until they are destroyed. Destroying them will greatly replenish any missing health. The same goes for the air mines, which you encounter part of the way through the stage.
After encountering a fifth bomber, you will be ambushed in mid-air. You will have to take down two enemy helicopters and two jets before you can resume the side-scrolling portion. Keep your aim around the middle of the sky when seeking targets. If you are fast enough, shoot down any missiles that get fired at you to prevent damage. When the four crafts are cleared, you will face an air mine and two more bombers before reaching the television tower.
The view will switch to a rifle scope as you prepare to take out the sniper in the tower. The first tower that you can see through the scope is not the television tower. Instead, you must shift your view to the left or right to find a tower that is much closer to you. At the very top, you will see a man peering out of the side. The motion of the helicopter will cause the rifle scope to move about. Get the crosshairs as close to the man's head as you can and tap until the view zooms in and steadies. Then press to take the shot and remove the sniper.
Upon success, you will be returned to the streets of East Berlin. This time, you will begin on the east end of the street by Brandenburg Gate. Start walking to the left. A man will suggest that you visit the Green Mansion. Several motorcyclists will attack you in this section. You will cross the Spree River shortly before being ambushed. This ambush will contain four men and two helicopters. As before, take out the four men on the ground first, then go after the helicopters. Just after that, you will reach the Green Mansion. A woman inside will tell you that Condor is meeting someone at the Potsdam Station.
You must walk all the way back to the place where you began Act 1. You will be subject to the same ambushes each time you return through the other two sections of East Berlin. Head inside Potsdam Station when you reach it, and Condor will appear. He will thank you and tell you that he has part of the vaccine file just before he is shot. Before he dies, he will tell you that the enemy's base is below the Spree River. With no alternative, it's time for you to return to the right and visit the Alexander Hotel. Be aware that you will still be ambushed by the four men on your way back for a third time.
Head to the Alexander Hotel (the second large building on the left side of the second section of East Berlin) and enter. The concierge will welcome you and inform you of Cherry Grace's room. You will next appear in her room, and inform Cherry that Condor is dead. With little else to do that evening, Golgo will spend the night in Cherry's room. The next morning, you will be back out on the streets of East Berlin with all of your health restored, in search of scuba gear. Such gear can only be found in one location: the Green Mansion. Fight your way back to the third section of East Berlin and enter the mansion. It turns out that Conder left scuba gear behind, and the woman allows you to access the Spree River through the mansion.