In the aftermath of Black Mesa's destruction, an eight-year old Alyx Vance along with her father Eli Vance flee to Europe and stay at a farm nearby White Forest. Alyx befriends a lonely Cow and they become close and the Cow acts as her guardian. Whilst out playing Alyx and the Cow come face to face with a man called the Director who offers them a role in a documentary he is filming and they innocently accept.
However the Director is a psychopath who plans on killing the Cow at a nearby meat factory. The Cow is close to being grinded up but Alyx saves her. They flee and the Director gives chase and tries to kill Alyx, but the Cow sits on him crushing the Director dead and ending his reign of terror.
In the epilogue, the Cow gives birth to baby cows and later passes away. Alyx raises the Cow until they grow up and become independent. Without a protector, Eli builds a robot to look after Alyx. Although Alyx wanted to call the robot 'Cow' Eli accidentally registers its name as Dog.