You are a U.S. Marine of the Hazardous Environment Combat Unit (HECU), detachment deployed to the Black Mesa Research Facility under explicit orders to interrogate the personnel and silence the facility. Being met with vicious attacks from Borderland Better known as "Xen" you were landed from the V-22 Osprey On the Surface of Sector D. along with other Marines, As they followed the command of the Sergeant Marines, so do you followed the command

Later moment before you head Inside the Black Mesa Research Facility, your squad is attacked by the Xen Creature, Alien Grunts, and Vortigaunts, you try to survive and kill multiple of them, The Xen Creature is extremely powerful, Only a few marines managed to escape, with some heading into the Black Mesa Research Facility and others to the empty hangar. However, you choose to go to the tunnel sewer next to the facility

You break through the tunnel doors and get inside the sewer, but you notice that there are Marines following you, you get deeper into the sewer trying to get off the vision of Xen Creatures, and you decide to look at the nickname of Marine following you behind, His name was "Corporal Adrian Shephard" Who carrying the M4-Carbine on his hands, and this gas-mask he also wearing It

Adrian sat down to calm himself, and you did the same, trying to clear the traumatic images you had seen: the explosion impact, Xen alien sounds, marine screams, and blood

As you saw the corpses of scientists and security guards lying on the water of sewers, with the heads covered with parasitic alien organisms from Xen named "Headcrab" you never knew this creature before, so you don't mind It but Adrian stopped sitting and he positions himself and holding the M4 Cabine on his hand, The Body of corpses of scientists and security guard starting to stand up and make the noise, It was Zombie Headcrab

"Contract!"

Adrian pull the triggers of his M4-Cabine, Shooting at the Zombie Headcrab and Killing them by his M4-Cabine, They keep coming

"Hey, What do we do!?"