After an accident with Engineer's new Australium powered teleporter, the entire RED team is teleported to a land where monsters known as titans rule the world and the human population is sent behind walls. What will the RED team do? Do they try to save the people of this twisted Earth or look for a way back home? Answers lay within the tale of Attack on Fortress!

When Gordon Freeman accepted the G-Man's deal, he had never expected his next assignment to be placed in another world where humans were hunted down and eaten by giants while backstabbers and undermines plague what remains of humanity. All of it tendering on a world on the verge of collapse and ruin, but the right man in the wrong place can make all the difference in the world.