Destroy the Tetranode with Strauss
Enter the elevator (#83) and travel down. Turn right to meet Strauss (#84). The engineer will explain to you that in order to destroy the core, it's necessary to do a few other things first.
Activate the Power Plant
Strauss has to run the power station and you're his bodyguard (nothing new). Go through the nearest door. Climb up the ladder located on the left side. It's leading to the chamber with some armor, but due to the fact that engineer is with you, it not necessary to collect it. Run straight ahead and kill all met enemies. Eventually you'll reach the room, where the panel activating the power station is located (#85). Wait until Strauss will use it, eliminate Gladiator and return to the elevator.
Find the Emergency ShutOff Controls
This time you'll run in the other direction. Actively participate in the fight with monsters. Thanks to that, you will protect Strauss. You will reach the elevator which will take you up. There, the engineer will use another control pad (#86) and complete his mission.
Shut Down the Coolant Pumps
Now your job to execute the last point of the destruction of the Nexus complex's plan. On the right from Strauss you'll find useful ammunition. Recover everything you can and go to the door. After short walk, safe and sound, you'll reach the big room with the panel in the middle #87). Make a save, choose strong weapon (e.g. Grenade Launcher) and prepare yourself for the fight.
After pushing the button you will be surrounded by two spiders (Stream Protectors), relatively though beast, that are using machine guns and flame throwers as weapons. Do not save ammunition - it won't be necessary later. When both spiders will fall down, prepare yourself for the fight against the final boss.
You don't stand a chance with the new Makron's incarnation (#88), but you can try your best. As soon as the big creature will stand up with you face to face, start to fire and avoid his bullets at the same time. Stroggos leader will get nervous. He'll use the other weapon to capture you.
Do not load a save game. Kane's not dead. But his life will never be the same.