《半条命：Alyx》是由V社开发的《半条命》续作，本次的故事发生在《半条命》和《半条命2》之间，是与邪恶的外星种族联合军之间看似毫无胜算的较量。玩家将在游戏中扮演爱莉克斯·凡斯，也是人类存活下去的唯一希望。

在黑山基地事件之后，联合军把仅存的人类圈禁在城市中，对地球的铁腕控制只增不减。人群之中有两位地球上最出色的科学家：您和您的父亲，伊莱·凡斯博士。反抗势力尚未稳固，身为发起成员的您，仍继续从事着秘密科学活动——展开至关重要的研究，为那些为数不多英勇抵抗联合军的人类打造宝贵的工具。每一天，你们对敌人的了解都更为深入；每一天，你们都在为找到他们的弱点而努力。

In the year 2043, Infinite Dendrogram, the world's first successful full-dive VRMMO was released. In addition to its ability to perfectly simulate the five senses, along with its many other amazing features, the game promised to offer players a world full of infinite possibilities. Nearly two years later, soon-to-be college freshman, Reiji Mukudori, is finally able to buy a copy of the game and start playing. With some help from his experienced older brother, Shuu, and his partner Embryo, Reiji embarks on an adventure into the world of Infinite Dendrogram.