You wake up somewhere underground with a shotgun and rifle. You don't have any clue about where you are, nor who you could be. What becomes clear shortly after, is that you are not alone and your inmates don't have a pleasant attitude. Your only option is to make smoking piles of meat from them. Fellow shotgun and rifle are ideal tools for the job. When you explore, you will find various memos about recent events. It seems like failed experiment with human beings. Classic. You want to get out alive and it will be a bloody journey. You must get trough several floors and be prepared to dance with mutants and other buggers. Also you will meet a task force unit assigned to alleviate the situation. Unfortunately you represent only another target practice, so remember your hunting skills. Be stealthy to avoid unnecessary conflict with zombies. When spotted run around the corner. Zombies are dumb and won't follow. Each floor has set time limit for completion, else be prepared for a thick opposition.