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This article describes the Half-Life: Decay storyline, chapter by chapter.

Dr. Cross and Dr. Green are members of a different team in Black Mesa than Half-Life's protagonist, Gordon Freeman. They are responsible for monitoring the equipment which Gordon uses during the experiment, and are in turn monitored by Dr. Rosenberg and Dr. Keller. Like Freeman, they are forced to fight for survival in the aftermath of the Resonance Cascade.

Chapter 1: Dual Access[]

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Rosenberg and Keller discussing as Colette Green and Gina Cross watch.

In the first chapter Gina Cross and Colette Green deliver the test sample to Freeman and activate the Anti-Mass Spectrometer, shortly before the "incident” (Resonance Cascade) occurs.

Chapter 2: Hazardous Course[]

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The training area in Sector A.

Gina Cross and Colette Green must escort Dr. Rosenberg through the Hazard Course area (Training Facility, Sector A) to the surface in order to call for military assistance.

Chapter 3: Surface Call[]

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Colette Green and Gina Cross making their way through the warehouse.

Cross, Green, and Rosenberg reach the surface with the objective of accessing the Satellite Communications Center. However, they find the front door to the Comm Centre locked, forcing Cross and Green to circle around through nearby warehouses to get to the unlocked back entrance. Once inside, they manually align the satellite dish and Rosenberg successfully contacts the military while Cross and Green head back down to Sector C.

Chapter 4: Resonance[]

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Richard Keller instructing Colette Green and Gina Cross on how to re-engage the dampening fields

Cross and Green return to Anomalous Materials and link back up with Dr. Keller. Dr. Keller decides that the best course of action is to re-engage the dampening fields, which he felt would end the Resonance Cascade. To do this, Cross and Green travel through the facility and successfully reset the secondary and primary dampening locks. However, the dampening fields fail soon after. Keller discovers that the failure was caused by intentional interference from the other side of the rifts and realizes that not all the aliens might be there by accident.

Chapter 5: Domestic Violence[]

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Dormitories South Wing, Level 3

Keller hatches a plan to create a resonance reversal using the prototype displacement beacon in the Gamma Labs. However, he needs a satellite in orbit before he can go through with the plan. Personnel in the High Altitude Launch Center are ready to launch the satellite, but due to a military air traffic lockdown that is in effect they can not. To remove the lockdown, an all-clear code is needed. Keller, Green, and Cross use the transit system to get to the nearby Level 3 Dormitories. There, they begin searching for a security guard with the codes. Their task is made more difficult by the fact that HECU soldiers are also present, and are busy eliminating science and security personnel. Eventually, the security guard is found. Armed with the codes, Cross, Green, and Keller travel to the Black Mesa Air-Traffic Control facility on the surface.

Chapter 6: Code Green[]

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Black Mesa Air Control

Cross and Green, after several fights with HECU soldiers and after successfully fighting off a V-22 Osprey, manage to secure the Black Mesa Air Control building. They proceed to enter the all-clear codes and lift the military air-traffic lockdown. They then return to Keller and head back underground to find a way to the Gamma Labs.

Chapter 7: Crossfire[]

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Inside Gamma Labs

The next task for Cross and Green is to manually raise the prototype displacement beacon in the Gamma Labs to the surface, so it can be activated. Keller reaches the main lab area, but cannot raise the beacon from where he is because of an obstruction. After accessing the labs via the drainage canals, Cross and Green travel through the lower levels of the labs, encountering and battling HECU soldiers and Xen creatures as they go. They reach the beacon, clear the obstruction blocking the beacon from ascending, and successfully raise the beacon.

Chapter 8: Intensity[]

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Inside Alien Quarantine Labs

Cross and Green return to Keller in the lab control area, where he gives them the task of activating the beam matrix system, which provides the power required for the prototype displacement beacon. To do this, they first take an elevator down to the Alien Quarantine Labs, which have become overrun by Xen creatures. After navigating through the labs, they reach the beam matrix and attempt to activate it while simultaneously defending it from Vortigaunts and Grunts, who are rapidly teleporting in. The beam matrix is activated, and Cross and Green return to Keller, who is making the final preparations for the resonance reversal.

Chapter 9: Rift[]

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Inside Gamma Labs with Rosenberg and Keller

Cross and Green are forced to defend the displacement beacon against a variety of attacking Xen creatures, including a Manta Ray. In the midst of the battle both characters are caught in what is explained as a "harmonic reflux" by Dr. Keller. It is during this sequence that the voice of Dr. Rosenberg can be heard warning that he "can't keep the portal open much longer," alluding to Calhoun's coinciding trip in Xen during Blue Shift. Dr. Cross and Dr. Green then return safely and Dr. Keller congratulates them on their success.

The resonance reversal presumably had the effect of severely weakening the resonance cascade. It still remains unclear whether the doctors managed to survive the nuclear explosion that occurs at the end of Opposing Force.

Bonus Chapter: Xen Attacks[]

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R-4913 and X-8973 retrieving the crystal stolen by Black Mesa

This is the bonus chapter of Half-Life: Decay. In it, two Vortigaunts named "Drone Subjects" X-8973 and R-4913 must retrieve the crystal sample which was used in tests (and stolen by the G-Man) in Black Mesa and take it back to their leader Nihilanth. It is also interesting to note that the level itself is connected to the parking garage as seen near the end of Half-Life: Opposing Force where the Nuclear warhead is disarmed by Adrian Shephard and rearmed by the G-Man.

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